I believe this is what you are asking for:
I have created three calculated fields using the existing logic you had in your Existing-New calculation:
Existing = ZN(IF [Visit] = "Accepted" and DATEDIFF('month',[Offer Date],TODAY())<=18 THEN 1 END)
New = ZN(IF [Visit] = "Accepted" and DATEDIFF('month',[Offer Date],TODAY())>18 THEN 1 END)
Unproven = ZN(IF [Visit]<>"Accepted" THEN 1 END)
The ZN() function converts the output to zero if it is null.
Dragged these calculated fields into your tooltip. See the attached workbook for the solution.
If it's what you need, please mark this as helpful or as 'correct answer' to close this case.
SoCal Territory MASTER v4.twbx 982.6 KB
Grateful for the swift reply and for introducing me to a new function ZN().
Thank you again for your assist.