Serial numbering of Lee-Enfield fore-end & magazine case
Different criteria was applied by different factories / countries / at different times. Anyone with copies of R.A.E.M.E. or A.E.M.E. issues in the applicable countries can provide a background; this of course applied to ordnance depots and unit armourers rather than the factories. Perhape Peter Laidler can weigh into this one too, from his practical experience.
One should not generalise on whether magazines or fore-ends were serial numbered at the factories. I have seen numbers electro-engraved on the bottoms of magazines that look like it was done at the factory. But in most cases they were stamped with individual stamps as a local armourer or workshop would do. Of course this does not usually transcribe to the No.1 rifle but can be found to flow through to the Nos. 5, 7 8 and 9 models as well. Again, the factory where rifles were originally produced comes into the equation along with the era.
Regarding serial numbers being stamped on the bottom of fore-woods, near the muzzle, it can work both ways, depending upon the period of time. This was done as bedding of the fore-end affected the rifle's shooting, so it was necessary to mate them up again after it was removed in the course of repair, refit or fine-tuning. The same applies to the No.1 (SMLE) rifle of course.
Enjoy your Enfields,
Ian