Do you really swap bolts each season, or are you using nuts and bolts interchangeably?
But more generally...why does everyone worry about the nuts getting worn, but virtually no mention of the studs (bolts) possibly wearing with age/use?
This makes no sense to me. A broken bleeder screw will not "stick" you, because it will not allow fluid to flow. It will actually warn you that you need to replace the caliper, but give you time to source one and do it at your earliest convenience.
Actually, I would much rather have the 50 or so ml of plain used oil staying behind than 50 ml of used oil contaminated with flush.
I don't know what standards prevail in Europe, but API requirements are reflected in this answer by Valvoline:
Motor oil manufacturers must meet minimum industry...
I spend a lot of time in Toyota and Honda forums and this is the first case of even suspected fakes from Rock that I've heard of. And those use a lot of NGK/NTK/Denso parts as OE.