In article , Amber Ormerod
writes

Maybe they need to have a fresh cut to be able to have the safe to eat?
Fungi cross infect very easily.

That seems very possible. Fresh cut, hopefully free of other fungi.
It may be that an already resident fungus would mean your new fungus
wouldn't establish, or it may simply be the practicality that your
average kit buyer might not be guaranteed to know the difference
between, say, oyster mushroom and polypore.
--
Kay
"Do not insult the crocodile until you have crossed the river"