Almost all Subs tend to hold their value because production numbers keep decreasing year on year. Some factors that particularly influence a vintage Sub's value: movement, dial, crystal, production numbers, famous wearers, rare production traits. Off the top of my head, I can't recall a Sub that was made in the 80's (either ref. or caliber) that attract a special value over, say, a new 2015 model. That's just off the top of my head.