There was no revocable/irrevocable clause stated in the last RIF notice, and you were gone, whether or not you volunteered, as your name was pre-selected. Why then would they now deliberately add the ‘irrevocable’ clause to this RIF notice, unless this is a big one, and they may want any and all takers, unlike the last one, when they turned down many volunteers. Of course, irrevocable means that you cannot change your mind, but doesn’t mean that they cannot still deny you if you volunteer.
But the last RIF seems to have been carefully orchestrated, in a conniving way, to deny many volunteers the opportunity of a package, then they wait to see how many would leave on their own, as some have, and many other people have also left. In all previous RIFs, very, very few volunteers get rejected. In the last one, however, the numbers were huge! The rejected volunteers knew that if they were rejected once, they may get rejected again; and no one expected a second record setting RIF so soon after the last one, so they chose to leave. And that explains this rapid succession RIF, just 2 months later. They saved a bundle on those that resigned, and waiting any longer to get rid of the rest will cost them.
Bottom line? The timing of both RIFs were pre-planned in advance.