nothing to do with what is perfectly OK, just what the IVA will look for.
8.8 or above on everything.
yes there are degrees of strength allowed to fasten non structural parts together, that is a judgement for the tester, if it is 8.8 there is no argument, stainless is A2-7, imperial three lines. there are bolts on a Zero that are imperial.
IVA requires "visible locking device", nylock, spring washer but NOT with flat washer, and yes they damage the surface of the part they are used on, best not used at all, snar washer less damage much better device, philidas nut.
Lock tight is not visible, so bolts fitted with it should be marked as such, you may be asked to prove it.
8.8 on zero master cylinder is vital, as is larger washer due to adjuster slot, lock nut.