From this thread and the lack of the copper recoil plates in Arlo's fore-end, are we to believe that some Lithgowicon rifles/fore-ends were manufactured without them. Or are they just missing?

If they're just missing Arlo, might I suggest that you just replace them by wood patching. If you can't do it, thgere will be someone nearby who can. Just follow the photographic instructions on a sub thread here. Afterwards, you'll have a nice tight fitting fore-end too