RoCKo hit it on the dot about the notch on the bottom of the 4 button strip shown in the pic NHM hyperlinked (3 large button for the sandtrooper pic RoCKo posted)
Doh!! If I only knew how to put arrows on pictures…
Although unseen in the ESB promo pic, the trooper on the right may have an unnotched 4 button strip. If that suit was sent off to Bermans & Nathans for the ROTJ suits, most suits on display by Lucas (usually ROTJ) don't have the notch. Just a guess.