Another deduction from these first principles is that where a court has previously pronounced an administrative interpretation of law reasonable, this determination is not binding on the administrative body in future. Just because the previous interpretation was held to be within reasonable boundaries does not preclude a re-evaluation of the statutory provisions in question.
Sullivan J. explained this point recently in Construction Workers Union (CLAC), Local No. 63 v. United Association of Journeymen and Apprentices of the Plumbing and Pipefitting Industry of the United States and Canada, Local 488, 2012 ABQB 540 (don't try to say it all at once...):
 Both applicants submit that the Board was not only interpreting its own statute, but also that it had to follow the principle of stare decisis. The correctness standard will apply if an issue is one of general law that is of central importance to the legal system as a whole and outside the tribunal’s specialized area of expertise: Dunsmuir at para 60. The proper application of the stare decisis doctrine fits within this description. However, I do not need to decide on this matter because, as is elaborated below, the doctrine of stare decisis does not affect the Panel’s decision in this case. The Board can alter its own precedents: see e.g. Health Sciences. Furthermore, the Court has merely decided whether the Board’s prior decisions were reasonable or within the Board’s jurisdiction to decide, not whether its decisions were correct on the issue of open periods. The Court has declined to interpret the relevant section of the Code. The jurisprudence developed by the Courts and referred to by the applicants does not address the question before the Panel in this case. Therefore, there is no question of whether the doctrine of stare decisis was correctly followed.The leading American case on this point is National Cable & Telecommunications Association v. Brand X (2005), 545 U.S. 967. The point is a bit trickier in the United States, because Chevron deference does not apply where the statute is "clear" (i.e. where there is a "right" answer) but I think the majority was on solid ground in explaining the correct position as follows:
A court’s prior judicial construction of a statute trumps an agency construction otherwise entitled to Chevron deference only if the prior court decision holds that its construction follows from the unambiguous terms of the statute and thus leaves no room for agency discretion. This principle follows from Chevron itself. Chevron established a “presumption that Congress, when it left ambiguity in a statute meant for implementation by an agency, understood that the ambiguity would be resolved, first and foremost, by the agency, and desired the agency (rather than the courts) to possess whatever degree of discretion the ambiguity allows.” Smiley, supra, at 740—741. Yet allowing a judicial precedent to foreclose an agency from interpreting an ambiguous statute, as the Court of Appeals assumed it could, would allow a court’s interpretation to override an agency’s. Chevron’s premise is that it is for agencies, not courts, to fill statutory gaps. See 467 U.S., at 843—844, and n. 11. The better rule is to hold judicial interpretations contained in precedents to the same demanding Chevron step one standard that applies if the court is reviewing the agency’s construction on a blank slate: Only a judicial precedent holding that the statute unambiguously forecloses the agency’s interpretation, and therefore contains no gap for the agency to fill, displaces a conflicting agency construction.One qualification should be added to the above. There are some cases, discussed by Sullivan J., which suggest that where an administrative body develops two divergent, entirely contradictory approaches, one of the two must ultimately be chosen (perhaps, the suggestion goes, by a court). But in the present case, the previous approach had been decisively rejected:
 I do not need to delve into this area of argument. In the present case the Panel is not creating a second conflicting interpretation. Rather, the Panel specifically rejects and overrules its earlier approach that allowed for the early closing of open periods. The Panel did not create a competing line of jurisprudence, but rather created a new approach to open periods based on its express finding that the previous jurisprudence should no longer apply. Therefore, pursuant to the Panel’s decision, only one line of reasoning will continue to exist with regard to the early closing of open periods. While I must determine whether or not the Panel’s decision to enunciate this new interpretation of the Code was reasonable, I do not need to decide which of the two conflicting interpretations is correct.Incidentally, Sullivan J. took 16 paragraphs to determine the standard of review issues. So much for the simplicity the Supreme Court of Canada promised in Dunsmuir! This time, the difficulty was in addressing the argument for the applicants that the principle of stare decisis is a legal question that attracts a standard of correctness. Sullivan J. correctly rejected this argument, and might have done so in shorter order had he proceeded from the first principles I have outlined, but his decision surely counts as evidence that standard of review analysis remains a tricky subject.
On the facts, which concerned the "closing" of open periods during which employees in a bargaining unit can be courted by unions competing with the incumbent, the decision that the "closure" was an unfair labour practice was reasonable:
 The Panel’s final decisions all fall within the range of possible acceptable outcomes. On the issue of open periods, the Panel decided that within the context of the case before it, only one outcome could acceptably uphold the goals of the Code. The Panel could have found that open periods can be closed, can only be closed with conditions, or cannot be closed at all. In detailing the judicial history of this issue it is clear that the Panel and the Courts have previously concluded that there must at least be conditions on when an open period can be closed, namely the requirement of informed waiver. However, the Panel provides numerous reasons why it felt in its experience and expertise that this approach was flawed. In particular, it found that this case was a prime example of how the Capital Care approach risks undermining other rights protected by the Code. The Panel therefore interpreted the statute in light of this and determined that in accordance with the purposes and other sections of the Code, labour policy more generally, and in line with other Canadian jurisdictions, open periods cannot be waived...
Here, the employer had been rapped on the knuckles. Given the risk of collusion between employer and incumbent union to deprive employees of freedom of choice, the challenged decision was reasonable. Keep your eyes peeled for an appeal. Furthermore, the applicant[s] challenge the Panel’s “strong reasons” for revisiting Capital Care. The Panel determined that its past interpretation of its own legislation was wrong, and identified numerous issues stemming from that approach, including in particular that the Capital Care approach was poorly defined, did not work when applied to a different industry than the one implicated in that case, and did not actually support the purposes of the Code but rather could be used to subvert them. All of these reasons support the reasonableness of the Panel’s decision to re-examine its past decision.