Yep, it depends on the loading how the WT+ cabin is used.
If it's a busy loading in CE, more than can be fitted in the CW cabin, then it's used as part of the CE cabin, with full CE meal service. Op-ups from Y to CE tend to end up in here.
If the CE load can fit wholly in the CW cabin, and there are more Y passengers than can fit in the Y cabin, the WT+ cabin is used as overspill from the Y cabin, with Y service.