I could be mistaken, but I believe only wins are recorded on a horse's registration papers.....that would explain why it's blank. Perhaps his previous owners also thought that meant he was unraced.
I must admit that I've known a couple sellers that would tell 'little white lies' about a horse's racing career. They felt show horse people were biased against horses that had been on the track, and that passing one off as unraced was the only way to ensure it a good home. Go figure.

But that was a long time ago, and given how easy it is to find a horse's record online, I doubt anyone can get away with it now!