Likely won't be a cabin number printed on it, and that's ok...
The tags are printed before your cabin is assigned, but the bar code on them is unique to you. Once
DCL updates your reservation with your cabin number, that will be part of the information available. If you'd feel better, you can write your cabin number on your tags, just be careful not to write over the top of something else.
Additionally, if you're flying in the day before (which is always recommended anyhow), you could walk over to the Disney transportation area and fill out new tags WITH your stateroom number as and use those since you won't be wanting to attach the other tags when you fly from home anyhow.