... owned this car for 24 years... carfax...shows the first time it was titled was 1991 with 29000 miles...
While CarFax was founded by two guys from Missouri in 1984, it was around 1993 before the company began to receive some sort of records from all 50 US states. Not complete records for every current and new vehicle event and not prior historical data, just that data events for vehicles from all 50 states were now being forwarded to CarFax as those events occurred.
State motor vehicle records were not in computer format. Same for insurance companies. If they were, records were not in a format to be easily exported. The internet as is known today did not gain popularity until the late 1990s. CarFax did not have a public website until late 1996. Website came about to sell the report directly to consumers. Previously, CarFax only shared their records with paying car dealerships via the traditional fax machine.
Depending when the respective state began an association with CarFax, I'm not surprised records for your car began in 1991. Have to start some where - records before that state began sharing data from its motor vehicle agencies and insurance companies are simply omitted.
You know the original dealership that sold the car. If you have not purchased a copy of the GM invoice to the dealership, you can add that document to your papertrail. purchase from GM media archives.
Paul at winvoices.com will create a masterful reproduction window sticker.
Additionally, depending upon the title requirements of that state, whether a car title is always required to sell a vehicle regardless of age or if the state's motor vehicle agency does not require vehicle titles for model years older than 25 years, you can contact that state's motor vehicle agency to request copies of the original application for title, copies of the original title, and any other records that agency has on file. There is usually a fee to retrieve copies of any records that may exist.
Many state agencies have a historic vehicles dept. Each would have a specific form to complete, have that document notarized, and return it with a copy of the car's current title document in your name as the requestor, showing ownership of that VIN.
Establishing a paper trail today for 1980s records would not be possible if the state does not require titles for vehicles older than 25 model years. Those records have already been purged from their databases. Some states do not keep title records older than 10 years. But some states keep title records and other documents on file as long as those records exist. Those states scanned the old paper records to microfische and/or microfilm before digital records existed AND have kept those records. Perhaps something to explore.