RSX is from early to mid '90s, was about Sora level in Shimano's lineup. So probably included in "sport" level bikes.

Rims began coming out without ferrules in the late '80s. They had reinforced spoke bed instead. Some rim lines included a OEM version of aftermarket rims that excluded the ferrules.

If the rim trues up well with acceptably even tension, no reason not to use them in less than extreme applications.