Nice collection, by the way. Like you, some of the most interesting stuff I have is from flea markets or something I've been to hell and back with.
The tang stamps are helpful in date coding but are definitely not the only thing to look at. Aside from the tangs, check:
.Scissors pivot pressed or screw (screw prior to 91/92)
.Corkscrew flouted or not (stopped in 70's or early 80's. Forget off top of my head)
.Large screwdriver /Bottle opener slip lock at 90° or not
.Whether or not the multi hook exists (91 or 92 and newer)
.Keyring - is attachment a shim, or does it fill a layer? Obviously a bail is even older.
.Height of layer division shims
.Backside Philips: does it have a can key slot or not? (80's to 92?)
.Bottle opener or Can opener metal finish in the craw area. (Older ones sometimes not so smooth, usually pre-1980's
.Cellidor scales, when removed, are more solid on older ones
.Tweezers handle material, metal or plastic. I dont tend to use that as the tweezers can be easily moved from one knife to another. But if everything else adds up old and the tweezer handle it metal, it's more of a confirmation
Metal inlays: Many are now hot stamped like more recent L.L. Bean offerings. Someone else can tell my the TYPE of metal but not me.
For what its worth. And please correct me if I am wrong