Vehicle Emission Sticker Under Hood

I own a 2000 Lincoln LS that has the 3.9L V8 that is clear and not disputable.
I even checked the VIN and it also stated that it is a 2000 Lincoln LS with
3.9L V8. However, the sticker under the hood says 3.0.
The mechanic lady at Wal-Mart says that the engine must have originally
been the 3.0 and was replaced with the 3.9L V8.
Yet I do not know if that is correct because if that was the case then the VIN
would show the car as being a 3.0L V6 yet the VIN matches the actual
engine in the car (the car clearly has the 3.9L V8 that is not in question but
what is in question is why the sticker under the hood shows 3.0 but the
actual engine is 3.9 and the VIN also says 3.9.
Is it possible that the sticker has been replaced. or is it possible that the
walmart mechanic is correct and the engine has been replaced. (but that still
wouldn't explain why the VIN states that it is a 3.9L V8
Please help me understand?
I can provide pictures if needed.