i think the lange datograph is a "known gem" as many have mentioned, but prices in secondary market doesnt reflect it , reasons being good brand, beautiful finishing, innovative movement and my dream watch
( not vested yet) but i have a gut feeling it isn't going to be so soon, but being intuitive after it gets so many mention here.
so are breguet dress watches - "unknown gems", for its inspiration for many brands mentioning tourbillon, breguet hands.....in their description column (vested )
VCs are gaining recognition though, they aren't perfoming too badly in auction nowadays (vested).
of course , all in my humble opinion.