Well , their durability greatly depends on the quality of the materials used in their making , and you cannot forget that even the highest quality materials are often ruined by the atrocious french brass rivets that bloat and disintegrate with time .I had to replace dozens of these over the years .
I'm much more happy with the 70's " vert armée " models that are of a stronger build.
Chromium tanned leather was the regular 1947 to 1962 material , the yellow finish you mentionned is plastified leather . It ages rather poorly .
By the way all of my bags came from the same producer . Here's the little anodised brass dot that is usually attached to the base of the steel frame :
It reads , in an abreviated version , " Lafuma , made in France , breveté sous la garantie du gouvernement " .