Looking at the vintage Trek site, in '84 the 400 & 500 series used an Atom Sport Helicomatic, and the 720, & 600 series used a Maillard 700 Helicomatic. In '85 a Lux Comp Sealed Helicomatic was used on the 620 & the 720 used a Maillard 700 sealed Helicomatic.
Maybe some of these were of better quality than others, accounting for the differing opinions people have of Helicomatics in general.