The one time I really sprayed the stuff on it got into the jersey and never got out. Well, it did, but it took like 2 years of regular use/washes. Since I use my kit all the time, even on the trainer, that meant a lot of washes.
If you do the light spray, wait, and stick, then it's better, no residue, but a chance of losing the number.
Since I use it for convenience (i.e. late to start) and no flapping, I'll sometimes put a pin or two on the leading edge of the number (after it's glued). Okay, I don't put them in, someone else does. But you get the idea. This way the number is flat but the wind won't peel it off my jersey.
I have 3-4 cans of the stuff and I've misplaced them all. So for now no Super 77.
cdr