I've heard disputes about whether the folding bead actually stretches.

When my folding tires get a bit easier to mount, it's because the rubber over the bead wears a bit, the rubber becomes a bit less sticky/tacky and the mold release goo wears off.

The tires themselves seem to stretch just a bit, so a folding tire is easier to remount after it's been used for awhile. That's why I'm waiting a week or so before switching my new pair of Conti GP Classics from butyl to latex tubes. I don't want to risk pinching a pricey latex tube. But after 100 miles or so, it'll be easier to mount. Ditto, Soma Supple Vitesse, Schwalbe One and other good folders. They get a little easier to work with after a little use.

But I'm not seeing any indication that the bead itself stretches. I suppose some clever engineer has done this -- stripping the bead out of new and worn tires to measure them. But I haven't read any reports on the results.