Found this chopmarked Trade Dollar on eBay. It has something I had not seen before; quite a few obverse rim cuds along the right side. It also has a die crack almost all the way around the periphery of the reverse.
I believe that the dark material in the crannies on the reverse is from storage in an old coin folder. There are stories about Trade Dollars being smuggled out of China in barrels of tar, but if that were the case with this coin, why is there no residue on the obverse?
It has plenty of luster, the chops are interesting, and PCGS graded it AU55.
Yes, sometimes test cuts were put into the rims to make sure it wasn't a plated fake. These are fairly common with chopmarks, however, many also went to India and were melted. Finding one in upper AU, or even MS, can be a matter of good luck. here are a couple more with chopmarks (one is bright from a cleaning)