It was kind of the wild west. You could import a horse, say you lost the papers, forge it a new identity, and no one was the wiser. Horses were getting shown in age-restricted classes that were older than they were supposed to be, though I think that horses shown in those classes were among the first to have a chip requirement. Now it’s kind of a two-factor ID as you have to have the horse, the papers, and the chip with all of them matching for those classes.
It was also pretty routine to have horses get sold and the new owner would just get a new USEF ID instead of transferring the ownership, quite possibly changing the name in the process. It was cheaper and easier to get a new one. Also easier not to provide USEF with the registry or pedigree number, especially if you waited until the day of the show and had annoyed people in line behind you in the show office.
One story. Vet scanned a horse a friend was buying during the PPE. Turned out the horse was several years older than advertised. We were able to get a copy of the KWPN papers and his European show record from the nice people in Holland. But, once he stepped on US soil there was no record because the name was changed at least twice.