This thread is starting to suffer from 'stitching issues', itself.
The Mobineko quote, which has been clarified, is @:
https://www.mobineko.com/vinyl-quality-standards/
'5. Physical pressing defects – stitching/nonfill' where you deal with both physical defects in one §.
Wheras,the Mossboss post was in the thread entitled, 'Stitching...pressing issue.'
https://www.lathetrolls.com/viewtopic.php?t=1974
The title of Mossy's reply was changed to 'non-fill', yet, among other things, Mossy does blame 'the material in the grooves':
'Note: PVC compounds today as not as tolerating as they used to be due to missing additives like lead and cadmium which has been banned.'
- Father José
Re: In need of tips, advice and suggestions for pressing records
A possible cause of the mis-connection being made (conceptually) between 'non-fill' and 'stitching' might be as simple as the grammatical difference between 'non-filling' and 'un-filling'. As mentioned, because some of the 'material' ends up on the stamper when one sees 'stitching' in the pile, it made the visible defect by leaving many tiny lacunæ that should (still) be 'filled' (w/vinyl). Whereas, 'non-fill' happened because the vinyl didn't completely fill the stamper's groove-channel, leaving much fewer, but much larger 'lacunæ' of (missing) vinyl, to begin with. So, it's as if there's non-fill, and then there's 'un-fill' - being when fully-flown vinyl is ripped off the pressing and stuck to the press's musical teeth. Remember the villain, Jaws?