It kind of sounds like you might be confusing sliding, expansion and extension. 7.G of the contract talks about it pretty well.

How many total days of vacation did you have? 3 days in July and how many in Aug? If you had 3 days in July, then I would assume you have at least 4 days in Aug. That means you are only needing to knock out one day of your 5 day carryover block of r days. The 48 buffer should take care of that.