Unknown or erroneous title on single axle fifth wheel

The DMV told me it's a homebuilt. I had a title from a deceased owner. It's date of"home building" was 1990. DMV had me track down the widow. I got my title as a homebuilt. No one challenging me yet...... however....truth is... it's factory built in the mid 70's. The mfgr serial number went missing somehow...it might be stolen .. but I got it when a renter moved out and abandoned it.