Current Population Of Unknown Cent Varieties

No they still show up. The last early date variety was discovered in 1995, the last middle date around 2002, the last late date (at least I think it will be a late date) 2011 and it will be officially announced and displayed at EAC this year.

If you're thinking of your 1881 IHC DDO/RPD, I hope that's a new one!
There are a lot of undocumented minor IHC varieties, but your 1881 is better than most of those, if there's a DDO too.
Some major IHC varieties, due to low survivability and/or expert scrutiny of collections go without discovery for even a century.
I have an 1870 Snow-8 with several dates punched in the denticles, that was first discovered in the 90's.
The biggest IHC variety, the Snow-1 1888/7, was not discovered until the mid-60s, due to rarity.

I stumbled across this in reading and figured I would share. Here are some variety comparisons from Snows first book in 1992, to those listed in 2009. I found it in the Longacre Ledger April 2010, Page 11. It should serve as motivation for those variety hunting!

Year 1992 2009
1895 7 32
1898 3 37
1906 3 50

The article does go on to say most of the additions to the print were known discoveries.