For some reason I'd had in mind that it was at the GM's option at release time - i.e. you could release a player who hadn't played, but they would not be forcibly moved from your roster to your prospect list unless a) they suffered a season-eliminating injury, b) they retired (in which case they'd be released wholesale), or c) they played overseas. If Ohlund and Johnson were not injured, did not play overseas, and did not retire they would be available at the GM's discretion. That plus the fact that, in my case, Johnson was listed as an eligible FA in the league lists, was enough to make me offer him a contract on the understanding that he'd be eligible for the HFNHL this season.
But hey, I readily acknowledge that my memory is far from the best, so I'm open to clarification.