Did you not get an antibody test at some point prior to the vaccine? That would have given you an answer with 99% certainty if you used a good one.
We would need some form of official recognition of antibody tests though. Pretty sure most places that require vaccination don't accept antibody test results.
In NYC, for example, they've been available for free at a ton of different sites. It may always be as convenient or quick, but it's free.
The half-life of antibody levels has been estimated at 73 days. The antibody tests are quite sensitive, time has not been enough of a factor yet to produce false negatives. In a year or two it might be.
The only time concern is that you need to wait 2-3 weeks until after you recover from COVID to ensure you test positive.