I have a bit of experience in the tractor industry. After reading this thread, I can almost guarantee I can explain what is happening (spoiler alert: no big conspiracy or "bait and switch.")
The OP is reading the engine serial number, not the tractor serial number. The engine was made in 2019 but was not used by the tractor factory until (probably) 2022. There were no L3902 models in 2019, so the tractor can not be that old.
The warranty will not be impacted as it starts based on the original sale date, not the manufacture date.
Now if the unit was faded, cracking, or otherwise damaged, the buyer should have called the dealer out on that before (or at the time of) delivery. The dealer may have shown him that exact tractor and discounted it (without saying so, as not to call attention the the problems) because of these issues. But before (or during) delivery is the time to discuss these issues, not weeks or months after you take delivery (just my two cents).