even the IRS says you can't defer on 'prior' comp. since it was impossible to defer on those amounts, I'd hold you could ignore those amounts of comp. this is different than a situation in which someone could have deferred, but simply started deferring later in the year.
Apparently, I am mistaken. For the Plans that stayed with Ascensus, the history did transport over. And for Plans that made the "right" decision to move away, Ascensus will provide the reports needed upon request.