In cases where recruiting say, special forces, means the character can not recruit more than say 5 of those soldiers because others are already using the recruitment center, would it be against the IR to say something like this:
Sir X,
There is no particular issue with recruiting special forces in general, but due to the many others already using our special forces center(s) you will not be able to recruit a suitable unit thus you should not recruit special forces currently.
With Regards,
If the realm has only 1 cavalry center but say 4 people already recruiting cavalry from it, it could fit in the same situation if there is an issue because I used special forces as my example.