forgive the interuption.. but why does it matter?
if you are buying an erb gun, it is likely a full auto sideplate gun. that means that you are spending a great deal of money on a piece of paper and that side plate. if there are any issues you can always take it off of that kit and put it on another. that said, the gun you are looking at could have been built by anyone if it was a sideplate that erb manufactured and registered before 86 and or even if it was one he made, you have no idea how hard it has been ridding in the last 24+ years.
erb guns hold a higher place in the resale arena than say catco and a few others because they were generally better. just like DLO.
in summary, the prices for these sideplates are as low as they were 5+ years ago and that is a great deal. go get it! if you need to rebuild it, you can buy a parts kit from a few guys here for around $500.
good luck.
rory
i made a few assumptions here so if any are incorrect, sorry. just wanted to address the bigger picture while still answering your question