If the OP were sincerely asking, there are many possibilities as to what is going on with the watch. I am no expert in anything, & in watches, I have never been a Tag Heuer person. Speaking generally, it could have been serviced by a watchmaker other than authorized Tag Heuer, it may have been repaired, parts may have been replaced, etc., but presuming the history presented here is all true, the real way to know is to bring it to Tag Heuer & ask. Every authorized dealer has been accommodating & helpful. When unsure, they all seem to have a standard policy of referring a senior staff member, arranging an appointment there, or at another location.
Chrono24 has historically consistently made good on backing up authenticity when customer service is contacted, they mediate thoroughly, review carefully & hold the dealers responsible.
Of course people have tried to sell fakes as Gen, more often on Craigslist (for those who enjoy life-threatening, cash-only parking lot meetings) or eBay, which at best I can say has been risky & strange at best. In the last experience I had on eBay with a watch dealer for IWC (second hand from a legit jeweler in Beverly Hills), the seller refunded my payment tagged that it was no longer available for sale, then asked me to call them to make the sale without going through eBay. I politely declined & explained that I made a purchase in a proper store. But they still called me consistently for three weeks, leaving messages asking to make the sale.
Chrono24 always holds sale funds in escrow for two weeks after the sale, for buyer protection regarding authenticity & representation. I have no financial or commercial affiliation of any kind with Chrono24, but I can say that my experiences with them have been excellent. Even if something is on Chrono24, due diligence is still important, study the details, request hi-res images, vet the seller, & finally have your new prize purchase inspected by a Gen dealer as soon as possible within the 14 day purchase window.
Unfortunately, another increasingly common reason for threads like this has been scammers “testing out” a fake they may be thinking of trying to scam someone on, by asking around rep boards in a “QC”-style way, making naive seeming claims about a watch, then posting photos to see what kinds of flaws people on the forums point out. The vast majority here are keen to this, but are still inherently helpful & knowledgeable people, so there’s no real need to dress up the story, it is a helpful community.
Cheers—