My part is DCC-aligned to Datums A, B & C (plane, circle, circle).

My print calls for Position of a diameter to Datum A and B (no modifiers) within .050mm, so I want to leave out Datum C.  

When reporting Position I have two options, use current reference frame or create a new one. If I use the current one, I'll be including Datum C (because the part is aligned to it already) but that's not what the print calls for. If I choose to create a new one and drag and drop just Datum A & B features over, it tells me Datum B can't be used because "Datum B is not an align type feature".

How can I evaluate position using just the first two datums?