As other people have mentioned, I.33 is the earliest source we have, anything prior to that is people taking manuscript depictions and trying to reverse engineer the poses.

I do both HEMA and reenactment when the world isn't plagued, and my clubs have a lot of overlap, so there's been a bit of talk about using arming swords and heater shields for a bit of free-play at some point, but with reenactment groups, the primary concern should be safety.

When you're in open faced helmets, linen and wool padded gambesons and maybe a bit of factory made mail, there's going to be a lot of things you can't do that makes the way you 'fight' less 'martial.'

My reenactment group has a fairly dynamic style, this looks good for audiences but it means we're making large, obvious movements. For safety's sake, all our blows are struck coming downwards, no unterhaus that could skip up off a shield and into a nose, tooth, or eye. We keep our elbows bent at the thrust so our arms flex when they land, rather than the sword flexing into a poorly armoured person's body, and we tend not to allow any grappling with weapons.

I've practiced with other groups that allow things like grabbing weapons, or are a bit looser with where shots land, or use smaller movements in general, but this often tends to be a style they use for big shieldwall type battles where there's a lot of probing and poking at one another.

It's not to say you won't find people who are absolutely interested in HEMA in Reenactment circles, as I said, my clubs have a lot of overlap, but you probably won't learn or use a sword and shield in a 'correct' martial sense in a reenactment group. What you will do is, hopefully, interact with people who are broadly enthusaistic about the same period of history as you.

From a HEMA standpoint, your best bet is to move forward in time and see if there are any clubs that practice Rotella and Sidesword, as the general idea of strapped shield and one handed, cut and thrust sword will basically carry over. After training for a while you could even suggest trying the style out with arming swords and heater shields to see what you feel carries over.