YHM has redesigned their rails on most/every handguard system they have - (I guess you could call it Generation II). On top of the fact that their new items are in very high demand from dealers on this board and others. YHM is also currently working on a large military order for an allied force.
They have added new tooling and more shifts to try to meet demand. I think there will be a extended lead time on certain products.
Best advise I can give, is if you want a YHM handguard rail product, get it asap when it comes up on the EE. We have delt with JTac and Brighflashlights and they are all good people.