My negs have been stored that way in my attic for about 40 years. I just dug them out and started scanning them, a couple of months ago, and they're all fine.

Consider this: when you pull one strip out of a sleeve, you're sliding it in and out,and both sides can get abraded; when you pull out a pile of strips, only the outer strips are sliding. Then when they're out of the sleeve, you carefully unpile them. That way, they are much LESS likely to get scratched, except for the first and last strip. If you sleeve them individually, every strip gets a chance to be scratched as it goes in and out. Unless you live on top of a jackhammer, once they're in the sleeve, there's no further risk.