Wow they must have had serious use.
I own two pairs, the 1983 ones, that have discoloured terribly, but are in A1 condition, no damage to the zips, and no tears.
The others, were bought in 1992 or there abouts and may outlast me.
The original Rohan Bags, as they used to be called, are almost identical in design, and the polycotton is very long lasting.