A little confirmation here. I bought a Jackson frame new in 1975 (don't know the year it was built). It had nothing in the way of braze-ons except the cable housing stop on the right chain stay for the rear derailleur cable. Wait, I take that back - it may have had one set of water-bottle cage bosses on the down tube - maybe. But certainly nothing else.

It also had long, pointy extensions of the bottom bracket hanger running up the back of the seat tube and the underside of the down tube. It had no cable routers at the BB - and it really could have used them. The tab on the seat tube stopped before interfering with the front derailleur, but the down tube tab made putting on a separate cable guide a major pain in the nether regions.

That bike was stolen out of my garage c.1992. But I am absolutely certain about the absence of useful braze-ons, again with the one defeinite exception and the one possible exception.