look at the back tag. if the numbers look like this: 505-0219, they are late 70s early 80s. if the 505 is printed in a different ink or looks different than the rest of the tag, they should be alright. the ones were the tag looks like it was printed as a whole, no variation at all in ink or sizing or placement, they are fairly new. these ive found are generally lower quality. look at the denim. i have a pair from the late 70s that have nicer denim than my redlines from the same period. very irregular, streaky denim, vertically falling. indigo holds up better too. also, look inside the jeans for the tag. try to find a pair that has the small tag on the outseam, with no batwing logo. should have washing instructions and "shrinks 3%" on one side, and a bunch of numbers on the other. thats another sign of 70s to early 80s levis. if there is no tag inside, and the zipper is not levis, then you have something older than mid 70s.