Is the box you pictured the one the Pietta came in? What is the date code on the Pietta? Also, you said the other two have COM under the loading lever, and Sile on the barrel. Were these sold as Euroarms? What do the boxes look like, anything on boxes, serial number match box, papers in box?
I have been trying to identify the COM marking for over 17yrs without luck. Some speculation but nothing concrete. If the two you have were sold as Euroarms this presents another question.
Your help would be appreciated.
Just in case, have you visited the Replica Percussion Revolver Collector's Association web site? If not you may find it interesting.
http://rprca.tripod.com