I first came across Framesaver about 18 years ago, but also used various sorts of shelac/waxoyl type stuff too. I've mended a few 40s and 50s frames full of some sort of black tar etc. so people were trying to rustproof their frames.
Even 531C or Columbus SL had thick enough main tube walls (0.7-0.8mm) that rust wasn't seen as a problem in the early 80s. Then along cane stuff like Columbus EL, Genius, 753, True Temper OX and Tange Prestige, with tube walls down to 0.5mm. A little rust could reduce the thickness by 20% pretty easily. Even the acid etch of chrome plating was seem as dangerous, hence the rise of stainless steel frame ends and lugs.
Down to 0.3mm on Reynolds 953 top tubes these days.
Similarly, chainstay walls have reduced from 1-0.8mm down to 0.5ish on plenty of the lighter steel tubesets these days.
Thankfully, many of the modern high grade steels (Nivacrom, Niobium, 853 etc.) are also pretty rust resistant. Framesaver's still a good insurance poicy, though.
Then of course there's always the fully stainless tubing Reynolds 953, 931, Columbus XCr and KVA.
All the best,
Pause, take a breath and ask yourself: "What would Rastamouse