If you select the whole domain (or main level OU) to license, the licensing tool will count “anything windows that is ENABLED” where you select. To reduce your count and what you have to pay for, you can do two things here:

• Option 1: You can select the whole domain, and manually subtract / declare how many servers you have. We’re reasonable people (enabling you to subtract up to about 10-15% of your overall count.)
• Option 2: You can cherry pick specific OUs which contain just client computers.

What happens then if you add OUs mid-year?:

• If you pick option 1, you wouldn’t need to re-run the tool mid-year if you update OUs. Since the whole domain is licensed, all child OUs are automatically licensed
• If you pick option 2, you WOULD need to re-run the tool mid-year if you update OUs. But it doesn’t cost you anything, unless you increase a lot of machines mid-year (20% of your current count). We would call that a mid-year true up.