More is known about 18th century silversmiths rather than 19th and 20th century silver platers due to the fact that the silversmith was registered with an assay office and was under constant scrutiny by the authorities. They generally held a high position in society, some where famous for their work, some infamous for their misdeeds. All these things and others, meant that records of the details of silversmiths are found in many places, but the same cannot be said of the silver plater, they, for the mostpart, did not not have to register, did not have to comply with laws. Sometimes they set up one year, and were gone the next, partnerships changed constantly in hugely completive industry, with new partnerships, often came new set of marks, and very often, different marks for different lines by the same company, pieces were made for other firms with yet again different marks, and next to nothing was officially recorded, unlike those of the silversmith.
The interest in plated products, especially that of electro plate, has until recent years been small, indeed, there was no interest in old silver until the second half of the 19th century, but now there is an ever growing interest in the work of the plating industry, and with that interest more and more research is carried out and new information comes to light, much of it generated by the internet. You asked "Where do we go to glean an identity?" , the answer is right here, by you and I and everyone else that share that interest exchanging snippets of information, like little pieces of a jig saw puzzle that eventually build into a more complete picture.
So, keep posting your found examples, and keep digging for information, it's out there somewhere.