STCs missing - huge gaps in records

I am still trying to purchase an Ercoupe and there are some issues with the records.

I spent hours pouring over what I have and made a spreadsheet of all of it to sequence the information.

Annual inspections look great and the shop doing the work over the past five years appears very professional. However, current and prior owners have not flown much at all, 82 hrs since 2008. ADs are complete and complied with. 

Records start at inception in 1946 and run to 1955 uninterrupted, then one entry for 1963, then a string of entries from 1977 to 2001. Then a gap to a single entry in 2008 when the c85 overhaul was done. Then one entry in 2019 and then from 2012 to 2015 I have records and in 2015 the Ercoupe had an accident - engine out due to contaminated fuel. There are no records regarding the repair of this accident and in 2017 records start up again to today and those records are very professional and complete. A lot of effort has gone into making this Ercoupe fly properly, but she hasn't been flown much. 

The question is how do I get the full list of STCs that are in effect for this airframe/engine, especially in regards to gross weight. The current W&B says 1260, but that does not mean there wasn't an STC for 1320 or 1400 at some point. I'd like to be on the same page as the FAA records and know whether this is a valid LSA. Once it is over 13230 you can't go back to LSA but I cannot determine that with certainty. 

How bad is it to not have all the records?