Interesting, how you guys see it.

You might have noticed, that little differences even on a dial of a watch can multiply the value.(like red writing, PN dials on a Daytona etc.)
This is not only true for a Rolex, but for a Patek even more.
On the 5712 the dial and the case are different. You just have to look.

You may have done right, if you had a 3712 and sold it for a premium. If your a dealer or cannot resist the money, that is.
I would never sell a watch like this, if i had one.

But you can make me happy and tell me, where to find one for 21k.