A category X vehicle is considered the most desirable of salvage categories because these cars have been subject to an insurance claim, but often while sustaining minimal or zero damage. Most commonly, this is because the car has been stolen, eventually causing the insurance company to pay off the owner. But it's my understanding that once the vehicle has been repaired, there's no record of the initial damage and cars are not recorded on the HPI register. If they are, they’re sometimes recorded under a different category - like Cat N. The fact that they’re not HPI registered can make it more difficult to look into the history of an individual vehicle. However, if you’re confident that you can repair any problems that may arise then it's worth considering.