All known Brown Old Mills are handcut or trimmed in someway. Some are very obvious some not as much as others.
I've talked with other collectors and from what we can confirm there are around 12 known brown Old Mills to date confirmed. It's safe to say that since we can confirm 12, just being safe perhaps maybe there's another 10+ or so out there locked away or not surfaced.
There are also cases of cards just being missed the recent Goodwin Sid Smith was not labeled as anyting other than AUTH, however collectors caught notice of the auction and the price quickly shot up. Oddly enough Sid Smith seems to be one of the easier cards to find as there are 3 of him known others not so much.
Another neat note brown Old Mills have only been found on southern league brown Hindu players to date and most likely are not found on Texas league players. All the confirmed brown OM's are also found with Brown Hindu.
Then there are the (3) known print oddities. Leon's own super cool multi-strike printers scrap is a Brown Old Mill (along with others). Finally we have the 2 known print scraps with Sweet Caporal OP that are known. The single OP that sold in REA and the double OP that sold in Oser in 98. These are the cards that Chan & the T206museum were producing to collectors as fakes. To read more in case you missed that see the below links.
http://imageevent.com/piojohn3/fraud...milloverprints
http://www.net54baseball.com/showthr...highlight=chan
http://bid.robertedwardauctions.com/...x?itemid=13341
If any of the info is a repeat sorry some of the newer members may have missed some of the info.
Cheers,
John