I was speaking even with invested items (the statement - it does not allow him to instill effects that he could not otherwise manage- in the text even pre errata rules out any use for lesser enchanted devices, and I'd never considered the possibility of using expiry on charged devices.)
Being able to accomplish 5 or ten seasons worth of work in a single season is really inherently abusive, but because we're talking about just one season of work it becomes much more manageable to bring in your sodales and other people's apprentices for laboratory assistance and this magnifies the problem. A character who has a lab total of 41 isn't going to be able to invest a level 50 enchantment in an item under normal circumstances, but if for one season they bring in two friends who have a combined int + magic theory of 14 and they use effect expiry they can knock out the level 50 enchantment in a single season.
This is close to the spell guideline I used, But I literally retrofitted WoMS.
So it's Level + 10 + stress die. So a Level 10 Spell will dispell a parma of 4,5, or 6 or even More (on Exceptional rolls from the stress die).... However making it specific not general this means the dispelling is on a Parma 1/5 of the spell level + stress die not 1/5 of half the spell level (or 1/10 spell level) + stress die.