Why is the Serial Number Missing?

[Singer B]

I recently acquired this No4 Mk2 from an estate sale. It is currently undergoing a deep cleaning and conservation process. It appears to be in really good condition. The serial numbers on the wrist, magazine, bolt handle and forward stock area all match. I cannot find the serial number on the receiver. I am beginning to think that possibly this rifle has been refinished and the receiver serial number removed? Your help and guidance is appreciated reference answering my question.