Scotch 770 tape types

I'm handling some tapes from the late 60s-early 70s and came across a curious situation. There are many Scotch 701 and 777 tapes in the lot with "yellow" labels, but on the single 777 "blue label" tape, I've encountered binder bleed something fierce. Running a reel through the tape cleaner at low speed leaves a coating of sticky goo on the cleaning blade and the tape where the tape motion stops. Fortunately, the goo can be cleaned off the tape with some 91% isopropanol; the same holds for the cleaner blade. This was with a tape that had spent a day "baking". Of course, there was no way this tape was going to make it through a drive without sticking to the guides or heads. I coated the tape with a film of cyclomethicone and reading was successful without issues. But I'm curious--I thought that a manufacturer's media type number should be the same, no matter when the tape was manufactured. Obviously, this isn't true--there's "yellow" 777 and then there's "blue" 777. Just a word of caution... --Chuck