I've often thought that (and wrote about it on here) how some appear completely oblivious to baldness up to a certain point.
I never knew how I'd put a number on it though, somewhat bald is not a topic that constantly comes up enough to get a good consensus. I can tell you on the flip side of this that some girls can spot an NW1.5 as if it's as gross as NW4.
It happened once when a few friends saw Facebook photos of a guy we didn't really like from a few years ago (may have influenced the negativity but still) and I didn't even notice his hair but one was instantly like "lol comb over!!!" And f***, she was right. It was subtle but there was a sweep back along the sideburns area going up his head, and then a flick down of hair over the temple corners. I didn't even notice before her.
Made me feel f*****g terrible about how she views my damn hair though.
It's case by case, if I was to guess I'd say you're right, up to a certain point women do not notice hair loss, depending on other factors like masculine face, forehead size, even head shape/size. For example I don't think many women would have noticed Jude Law's hair loss until even past BW3, but not just the top tier good looking but some people's head shapes let them away with it.
Here's a somewhat related interesting case, Mark Lamarr:
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I've always meant to discuss this guy on here. Damn good density no doubt, but temples are really confusing to guess how bad it is, he's minimum NW2 but arguably as bad as 3.5, his forward side burns give a strange illusion.
But the hair line itself above his forehead is pretty sh*t. I still don't think with his head shape and damn ballsy sweep back that most women/full heads would even think of baldness, even though that forehead is pretty damn big.