what was the last year for just lap belts?

bought some chrome buckle lap belts for my 67 a few years ago - couldn't find OEM
ones. Anyway, think the lap belt has a tag on it that tells what year you had to start
using sholder belts. 68 I believe, The web site I bought the belts from should also have
that info - just google lap belts and look at one of the vendors that sells them.