When does Interest Start In Delayed CAT Benefit Disputes?

The Court of Appeal recently considered the issue of when interest starts to accrue under the Statutory Accident Benefits Schedule  in situations where there is a disputed catastrophic impairment designation ("CAT").  In Van Galder v Economical, the insurer paid attendant care benefits and housekeeping/home maintenance benefits until the two year mark and stopped at that time based on the fact that the claimant was not catastrophically impaired.

A few years later, after the insurer completed its own CAT assessments, it agreed that the plaintiff was catastrophically injured, and retroactively paid attendant care and housekeeping/home maintenance pursuant to its obligations under the 2010 SABs, which were amended to oblige an insurer to make retroactive payments without regard to when the insured person actually became catastrophically impaired. The question remained though – what about interest?  Was it due retroactively as well, or not payable because the benefits