Darren,
Methinks you are getting confused.
When working with involute cutters, there are actually 8 cutters in each set, you select which cutter you require for the number of teeth needed on the gear. So say you require 23 teeth on the gear, you would use #5 cutter, or for 46 teeth #3.
8 cutters make up a set for one sized tooth.
To make a larger tooth, you will require another set of 8.
Myford use 20 DP for their standard sets of gears, so you would buy the full set of 8 cutters to make a set of change gears. It would be the same if your lathe or whatever used say 14 DP. Another set of cutters to your growing collection.
It is for that reason I will soon be experimenting with gear hobs. One hob of say MOD 0.8 will cut the whole range of teeth. Whereas for involute, you will require 8 cutters.
John