The Verbiage in Reconstruction is R day Blocks, plural, they are only going to have a Single R day if they are required to do so.
For Example, if you had a larger Vacation period and the Extension+Vacation days added up to 18...then you'd wind up with a Single R day.
Otherwise, they could only use you on an O&B trip or pay the Overage if they launched you.
One mistake people occasionally make in a Reserve Vacation month is being sick for the 3 or 4 days they have left with the expectation that they'll only be charged SL if assigned a trip...but, it's one of those things that if your Sick for Every R day you Could be launched on they charge you for the whole block