Strictly, what makes the Spin Turn 'Underturned' is entirely down to the amount of turn made on step 4 (the man's pivot) and between steps 5 & 6. It has nothing to do with what precedes or follows.

When the Turn is underturned, the amounts of turn are 3/8 to R on step 4 and 1/4 to R between 5 & 6. This turn can be made either at a corner, or along the side of the room, but the standard amount of turn is 1/2 to R on step 4 & 3/8 to R between 5 & 6. This amount of turn is only danced along the side of the room.

Hi Telemark,
I believe we all know that you intended to write, 'R' instead of 'L'.

Duh! Yes, now corrected!