That's the thing about serial numbers.
They don't always start at #1 and move along sequentially.
In the Case of the Mountain Rifle they did have #1 and 2,, there was a gent here that got them from an estate auction in un-fired condition.
But serial #'s can be a date, an order#, a machine or line or even an individual assembler at the plant.
They switched building the MR from the USA for the first few 100, over to Spain, and Deer Creek made some of the original MR and still make a copy of it,,
Having a low number I guess is proof that it's an older one but the list of when/where and how has been long lost, even many of those that were at the beginning of the CVR MR has since past and the info is gone with them.
We've been trying for years to find links or data and no-one has yet, :idunno:
Good luck, if you find something let us know.