That's correct currently if you have booked using the stay plus (even for a booking months in the future) you are not currently able to search any other stay plus dates across any properties.I assume if you’ve used a stay plus for a future booking you can’t then check if there’s a better deal elsewhere or at the same place?
As of the 1st of October when we change to the new system this is no longer an issue as you can use it across pretty much any non blackout night.
Will the new Stay Plus FREE Night be subject to allocation and availability?
"With the upgraded ALL Accor+ Explorer programme, the Stay Plus FREE Night benefit has seen some improvements, so it's no longer subject to or limited by allocation. This means you can enjoy this benefit more freely, whenever and wherever you like."