the blue line is the NYA(148) people agreed to the NYA meaning the blueline(148) reached its threshold and activated.
part of 148 is to ignore old blocks on august 1st. and guess what happened on august first BCH
if you want to pretend there was no chain split.. then you are ignoring the existance of BCH
if you want to ignore that 148 and 91 happened then you are ignoring all blockdata of the 2017 time period that contains the mentioned flags in those bips.
so instead of shouting a narrative of a story you were told by a buddy.. try using blockdata and also actual bips..
You ask to discuss about the block data.
Does Bitcoin blockchain "know" about BCH splitting off? I don't think so. According to bitcoin's blockchain BCH doesn't exist.
That BIP activation and the split is recorded probably on BCH chain, which doesn't matter in this discussion, since we talk about bitcoin, not altcoins.
So, I may be wrong, since I don't know the things that good, but imho you are also getting into the discussion things that should not be there.
It's all about how one looks at the things.