I was told Very Emphatically by a shop owner that all cotton thread should be thrown out after 3 years.
If that were true, how could there be any old quilts or old clothes?
Many of us have been through the “polyester cuts through cotton fabric” era. Is the 3-year “rule” for cotton now the rationale for using poly thread?
I would not use old thread I had not stored, myself, but beyond that, these sweeping generalizations are very irritating.