Hi Jim,
For my understanding, when you directly buy Office 365 Plan p1 or apply for a Plan P1 free trial, you will see figure below, it said “For small businesses(fewer than 25 users)”, but Plan P1 says they can support 50 user maximum. Are you confusing these two number?
In fact, when you complete all registration of Plan P1 and log into MOP, you will find that you can purchase more than 25 licenses.
More detailed and accurate information about purchasing licenses, I suggest you contact sales and billing team via links below:
http://onlinehelp.microsoft.com/en-us/office365-smallbusinesses/ff652569.aspx
http://virtualchat.support.microsoft.com/client/default.aspx?siteid=32ECF580-B446-44E5-8B4D-25F0AFE07779&scope=billing&query=Billing%20Support%20phone%20number
Thanks,
Jacky Ding