Not being lazy here, I just can't find it. Do you have a contractual reference?

Depends on what type of XX day moves we're talking about. If you are inferring that people want to use their 13 off days as 1 day off every 2 or 3 days then I agree, Delta cannot run an airline that way. But moving a group of days from the middle of a large block to somewhere else, and the new schedule conforms to 3-99-5 or whatever the category rules happen to be should not be a problem. Assuming enough open RES days you can already do that, but it takes 2-3 PCS runs. Often I find myself in the situation where my end-state would be legal with proper RES available but the in-between steps of getting to that point I run into not having enough reserve coverage OR I'd have to give up a weekend of XX days knowing that once I move those, I won't be able to get them back since the REQ is already lower than the available. That is extremely frustrating and doesn't make any sense whatsoever.