I have a 1970 that I have traced the ownership back to 1981.  I've spoken to each of the previous owners.  The vehicle was purchased in 1981 from a for sale by owner newspaper ad in the Sarasota, FL newspaper.  The Vette is now in PA.  Is there a way I can find the original owner through the VIN number by contacting GM.  I know the vehicle was originally titled in FL.  I contacted the FL Dept of motor vehicles, paid the $15 fee, but the records are in electronic format for only the past 15 years.  They aren't interested in researching the paper files.

GM will not have any information on this. Most states that do offer the title search will only go back so far, as you found with Florida. Your only other option, if a title search doesn't go back, is to place an ad in one of the major trades, like Hemmings.
I see ads in the NCRS "Driveline" all the time that start something like..."Anyone recall seeing a maroon, big block, '72 running around in the Detroit area in the mid 70's?. Would like to locate original owner".
While it may seem like a long-shot, you just never know.

Like geneology, you may not want to know the POs. Might be a horse thief in the history.