No, the electropencil was indeed done at the arsenal and not by Century or other importers. For one reason, the electropencil is the same from one importer to another, which would be very strange for RGuns, Interordance, Tennessee Guns, Century, and Aztec to be all doing the same thing in the same way. The exporter is not doing this because when they did want to fake numbers, as in the fake snipers shipped over, they stamped the numbers, not electro-pencil. And, these were sold so cheap that it would not be worth the time nor effort to electro-pencil them to make them match. What's more, these rifles are still covered in cosmoline.
This same marking is evident on SVT-40's imported 10 years ago in a completely unrelated shipment. They were refurbed at the same time as the Mosins, though (and the K98k's that are also electro-penciled).
Now, there are several importers currently using a dot-matrix impact style marking scheme for adding new serial numbers as mandated by the ATF on the receiver as well as the importer name. But this is very clearly done by machine whereas the original electro-pencil is done by hand. These two methods are completely different.
Ash