I can’t speak for all manufacturers, but some will use 8 iron specific shafts, trim them and brand them as a wedge shaft. Others will simply develop a wedge specific shaft for whatever kind of performance they are trying to get to. Better players will experiment, a lot, with different wedge shafts or iron shafts trimmed a certain way to get the performance they are looking for based on their own attack angle, ball type, etc. Several schools of thought on wedges, whether they should be more flexible (my view) or stiffer than the shafts in the irons. Still, to each his own and you just have evaluate and test to get the right trajectory and spin for your game and the conditions you play in.