Update: I ordered six of the 3089nnnn food container parts from DS and they came with the stickers in place. Looking carefully at how they have been applied (and having done quite a few of these myself!), I believe they have been applied by hand not machine.
Firstly, the stickers were not all started on the same face of the plastic part (the photo shows the overlapping end of the sticker in all 6 cases). This could happen with a machine because (some of) those plastic parts are square in section and it would not matter which face the sticker was applied to first.
Secondly, the sticker is higher up the part in some cases and lower in others. Again this could be caused by machines with different settings.
Thirdly, one of the stickers is not even straight (on the right hand, green container).
If these had been applied by machine, I should have thought there would have been greater accuracy and consistency. So until someone can tell me different, I believe PM are using human labour to apply the stickers.
But why? PM sets almost all come with some final assembly to be done by the end-user, often with stickers to be applied, so why make an exception for these parts? It cannot be cheaper, surely?
The only reason for using pre-stickered parts I can think of is that it saves having to include instructions on how and where to apply the stickers, as in the reissued instructions for set 3200. For a small set which otherwise needs no instruction sheet, this might make sense, but I shouldn't think it happens very often.