Thanks for the advice, guys! Understood that clipped tangs and filler is a perfectly normal way to do a fretboard.
When I noticed the off-colour filler on the PBG neck I realised that I literally couldn't remember what the side of my old guitars' fretboards looked like, so checked my LPJ -- the only electric I have now -- and it doesn't have any visible filler, and what looks like the full height of the tang (1.5mm or so) is visible:
Attachment 33749
Then I checked a bunch of photos online of Tele fretboards, and they all looked like they were the same as the LPJ (though to be honest it's bloody hard to see -- photos of the sides of fretboards are surprisingly hard to find!). That, plus some vaguely-remembered Crimson Guitars videos had made me think that it was always visible-tang or bound
But now I know that there's another way, which happens to be the way this neck was designed. I *knew* this guitar-building lark was going to teach me stuff :)