The RSPCA found Sauvage and County Hall — both by Saddlers' Hall — together with four other horses at a property in Yorkshire in mid-July.
County Hall was recorded as dead in April 2007, while Weatherbys was notified about Sauvage's "death" in January 2008.
The horses' identities were revealed by their microchips — it has been a requirement for all registered thoroughbred foals to be chipped since 1999.
"Microchips have proved their worth in this instance," said Paul Greeves from Weatherbys.
"After scanning the microchips we verified their parentage through DNA profiling — which reaffirmed their identity.
"It is not the first time a thoroughbred has been reported as dead when they are not, but it's rare. There can, of course, be mistakes, but with microchips and the stringent rules now it is fortunately less likely."
Di Arbuthnot from Retraining of Racehorses (RoR) added: "Microchips are hugely helpful. I very much hope that no similar cases come about, but at least we are now able to trace and identify them.
"RoR aims to prevent things from getting to this stage by giving racehorses a new life, so they won't end up on a scrap heap."
Who notified the horses as dead, and why, is unknown.
Although nine-year-old Sauvage, out of Gallic Honey, and seven-year-old County Hall, out of Awbeg Beauty, are both by the same sire, Mr Greeves believes this is coincidence as no other connections between the two have been established.
Neither horse had been registered as being in training and neither had raced.
The pair have now been issued with duplicate passports and are in east Yorkshire under the care of the RSPCA.
Starts with an 'S,' ends with a 'T.' You figure it out.
"Houston, Tranquility Base here, picking up where we left off ..."
I bought a dead horse from the auction once. I traced him through his tattoo and tracked down the breeder, who was absolutely shocked to hear from me. She had sold the horse as a yearling, followed him throughout his career, then heard he had wrecked a sesamoid and been but down. The first part was true--he did have a wrecked sesamoid, and he was declared dead to the JC. From what we can figure, the trainer sent him to be put down and someone deviated him to New Holland to make a few extra bucks. I bought him a little more than a year later at Eyler's. I figure the person who bought him from NH figured that he might come sound with time, then made a little money running him through Eyler's.
Life would be infinitely better if pinatas suddenly appeared throughout the day.