I think also that condition is more important than a low number, PROVIDED the low numbered rifle and the one higher are mechanically identical. I suppose a gun with a single digit number would command a premium over a similar but identical later version, and the level of that premium would be personal to a purchaser on the day?
A genuine No.1 would be quite a different proposition however.

As an aside I remember a well known dealer telling me that some Webley air rifles sold in the late 1980's/early 90's were often made with more than one serial number 1 ! Presumably so several No.1's could be presented to 'friends' of the company?

Rather cynical really, and there are no doubt owners of No.1 Webley Eclipse I think may have been one example, who are rejoicing in the albeit mistaken knowledge they own the very first.