If they still smell fine, and if they swatch as smoothly as ever, they should be fine.
When some lipsticks are old, they don't smell rancid, but they get hard and won't apply as they should, so that's another way to tell. But it sounds like yours are still ok. If something LE and/or in special packaging goes bad, there may be some collector who would want them, even if they can't wear them.
I throw away the old mascaras and ordinary colored rancid lipsticks. But I have a box of "museumized" makeup, stuff from companies that are no longer around (like Mary Quant and Biba) and some other fun stuff (swirly multi-colored lip glosses in pots from... the 80s?). I've also saved old lipsticks when i wanted to find a dupe, so i could bring them with me to compare.
My Grid and Lust were OK early in 2012, but they finally went bad a month or two ago - and they were from the mid 90s - so they lasted around 15 years. Because of their unusual colors i'm going to "museumize" them.
Did Grid and Lust go rancid or get hard? That's crazy they lasted so long tho. What finishes are they?