I know next to nothing about manufacturing and QC but surely the manufacturing process should be one that only rarely results in these unsightly marks. Perhaps we could argue that the manufacturing process for Jet Pluses is just not ready for prime time yet? It would explain the acute shortage, and it would explain why the 4.7" models are relatively plentiful whilst the Plus is nigh-on nonexistent in inventory despite them having the same finish.So one week 39 unit doesn't have the machining marks and another week 39 unit has them. Sounds like inconsistent QC.
The only pattern we've seen so far is this seems to affect mostly the Plus units. Hopefully Apple will eventually get around to fixing it.