My apologies: I was looking at your pics on my phone, and didn't catch the A versus B on the serials. No, that is not normal. I downloaded your pics and blew them up as best as I could on my laptop, and it still looks like the serial is original on the bolt with the A. It is curious, and I can only speculate that somewhere way back, a mistake was made where the A was struck instead of a B. Or... rifle 5132A had its bolt swapped with rifle 5132B. If you can provide a closer, higher resolution pic of the bolt, perhaps others can weigh in. If is smells like cold-blue, then you know it's been messed with.
Either way, I'd be happy to own it.