Sure, if they fought at those historic times with no weight limit, and if they beat HWs like Severn, Shamrock, Conan Silvera, Kimo Leopoldo, like they did, then they are legit HWs when we look at those historic times. And should be considered as good wins for HWs at those historic times, because they showed abillity to beat them. If you beat Royce Gracie in 1990s, that is a great HW win.
There was no minimum weight required, or anything. No weight limit at all, up or down. If you can beat good big HW fighters, you are a HW, no matter what you weight. You showed your fighting abillity. At the end of the day, it is a fight where abillity to beat the other guy counts, not a weight in contest where the bigger number on the scale automatically wins.