One of the few remaining unresolved limitation issues of real consequence is whether s. 18 is a deeming provision (it’s not) or merely alters the s. 5(2) presumption (it does).
Justice Charney’s decision in Gendron v. Thompson Fuels contains one paragraph (out of 431) the tends to support the latter interpretation:
 I agree with Thompson’s position that the limitation period began to run on June 15, 2010, pursuant to s. 18 of the Limitations Act. At that point Mr. Gendron knew that he had a potential claim against Thompson Fuels for contribution and indemnity for the s.100.1 order made by the City. I do not accept the plaintiff’s argument that the limitation period did not begin to run until the ETR process had run its course. Section 18 specifically provides that the limitation period begins to run “the day on which the first alleged wrongdoer was served with the claim in respect of which contribution and indemnity is sought”, and there is no dispute that Mr. Gendron was served with the City’s order on June 15, 2010.
By this reasoning, it’s arguable that if Gendron had learned of the potential claim for contribution and indemnity on a date after service of the City’s order, then the s. 18 limitation period would have commenced after until that date.