Like I said on Discord:
I think if you bring in the right material, it will already be inocculated with everything.
If you bring in dead organic stuff, you can bet that all sorts of spores and whatnot are already present on the surfaces.
Mycorrhizal fungi are around forever. Since the first plants grew on land.
Some say, these fungi made it to land even before plants and allowed plants to conquer land.
Anyways, they are omnipresent; spores last forever, the fungi blasted spores into this world for many millions of years.
These spores and all other 'micro' life is already present in any soil that you recover from the big outside
For a mycellium to form (or any other 'soil food web') it takes the right nutrients.
And like I said in the beginning: Whatever the material you bring in, the stuff that wants to eat away at it, is already present on the piece, just waiting for the right conditions to multiply.
Or the other way round: If you don't find the mycellium around your plant that you wish for, you should focus on bringing in the material it feeds on.
I went down the mushroom rabbit hole deep.
I did a lot of stuff with grain. I went through a complicated process of steam-sterilizing the grain and whatnot, worked super clean. Even then: If I wasn't careful, something else would colonize the grain. Whether some spores or germs or whatever survived 20 minute high pressure cooking or the bleaching of the utensils or whatever....
I came to the conclusion, that fungi and their spores are literally on everything.
So the job isn't really to bring in fungi, but to create the right conditions for them. And if you don't have fungi, then there was nothing for them to feed on in the first place, or they got outraced by something else that got to the nutrients first, and then that's ok, too.
Bottomline is: you want something to break down material to provide nutrients for your plants. I wouldn't worry if that isn't necessarily fungi or more specifically mycorizzae. Because the material you used as substrate didn't need fungi is why they aren't present. And actually they are present, they just did not go to work. Or they did a week earlier, before you looked and now something else is active...
I should have written a post...