换发动机问题求教, 老猫请帮忙

老猫班主各位大虾:

My Toyota 2004 had an accident and the engine was replaced by a Toyota dealership with another used engine. The first 11 digits of the VIN number on this engine was wiped out, so that it would be very difficult to get detailed information on this engine, including the year made, mileage on it, and so on.
Is this common practice or it is suspicious?
What should I do?
I have the car, it runs OK, but I haven’t pay them yet. So I can negotiate with them for a reasonable deal.
非常感谢!