On government rifles, it's an assembly number, to keep the parts together. On commercial rifles...who knows? It's a topic I'm still researching. Every time I come up with a new theory, I get new evidence that debunks it.

Does the bolt handle have anything stamped on it, either on the handle or bottom of the cocking piece?

If you're planning to remove the wood, there may be some marks underneath the fore-end that can tell us more.