You will be able to get good information on the Ericson owners website, which includes lots of knowledgeable owners including at least one who worked at the Ericson factory and has lots of knowledge about how they were built and what to look for in the different models. I'm sure they could help you determine if it is a "factory" Ericson, or something less than that.
In general, Ericsons are very well built boats, and as others have said, if you are happy with the boat, don't see any major problems with it and she sails well, then that's probably all that counts.
Good luck!
Frank.