What's the difference between French, Belgian, and Italian linen?

All three refer to where the flax is grown or woven, not necessarily where the sheet is sewn. French (especially Normandy) and Belgian flax are the two most-cited as premium in the signals we read, thanks to the climate of the Flax Belt. Reddit threads also single out Irish linen as top-tier. In practice, 'French flax from Normandy' on a label is a meaningful quality signal; the country of finishing/sewing usually isn't.