My Take is that these were the discards
You make a stone tool and give it a test straight away. Maybe it works real good, but maybe it doesn't. In those days they had no QC or TQM (Thank goodness). So if a tool proved not quite up to scratch, you'd drop it after the first trial and go make another.
When you got a real good one, THEN you kept it.
(How many of us have a favourite hammer or screwdriver that we use most of the time 'cos it just fits our hand right?)