Data Validation "avoid Duplicate And Non Specified No.s"

I have a list of buses numbered something like this 320-360, 700-750, 800-899, 900-990. (but not always consecutive ie... 325 may be deleted). each day I want to enter them into a worksheet call "Shed" ( cells B3:E46) which is how they are parked ie.. bus 320 in B3, 321, in B4, .... bus 700 in E3, 701 in E5 etc....

I only want to be able to enter the bus number once so it won't be allocated in the shed more than once. (the code below provides this, but it also allows entries between the lowest and highest numbers which is not suitable.) The numbers are listed in column M to R

=And(Or(And(B3>=$M$2,B3<=$M$250),And(B3>=$N$2,B3< =$N$250),And(B3>=$O$2,B3<=$O$250),And(B3>=$P$2,B3< =$P$23),And(B3>=$Q$2,B3<=$Q$23),And(B3>=$R$2,B3<=$ R$23)), COUNTIF($B$3:$E$46,B3)<2)

The numbers will also change after time, numbers will be added to and numbers will be removed. I hope I haven't waffled on too much. but that is basicly what I was wanting to do.