Hi Paul,
If you’re certain the bonnet has been replaced then it has been replaced with a bonnet from another car.
The experience with my car is that the bonnet had been replaced after an accident well before my ownership as it had no body number stamped on it.
It was in such bad shape (8mm of body filler in spots) and beyond repair, I had to find a NOS bonnet out of Germany and grind its edges to fit. You’re lucky the donor car’s bonnet fitted nicely as I’m sure you’re aware, these cars were hand built and the bonnets were shaped to fit each individual car.
I’ve attached a pic of the sad state of my car prior to me restoring it. You can see the bonnet edge in top. The more I dug, the worse it got.
Doug