Renew your old duplicate boards with these red labels with the word VULNERABLE marked in white.
PLayers need 8 vulnerable stickers for each set of four boards. For example "vulnerable' stickers for 24 boards will require 6x8 = 48 total. If customers want the red inserts for the boards they will need 48 of those also.
Be sure to label them properly.
If you ask we can send a convention card with the order that shows how each board is vulnerable or not. The non coloured part of the convention card lists the boards 1-36 and who is vulnerable for each board.