Perhaps I was not clear in my post... most B12 production has focused on the "bacterial" production and absorption... pancreatic enzymes among others being necessary too... a weak link in the chain and we have a problem with production and/or absorption, and may likely need to supplement.
In fact levels of B12 absorption have been shown to fall with impaired pancreatic function and removal of all or a part of the ileum, etc. etc.
My guess is that any one of us modern humans have probably fallen in our ability to make and/or absorb nutrients for one of many reasons or another.
B12 has been found to be produced by gram negative and positive bacteria, both rod and cocci forms, yeasts and molds.