Could "a" be a ligature?

[Koen G]

I'm usually of the opinion that exceptions in a handwritten text of this size should be treated with caution. Otherwise I'd say this is some evidence that both the a-curve and the n-swoop are minim modifiers. And since those are positionally determined, they don't mean anything, lending credibility to the Roman numeral-like idea.

But these are exceptional, and we have no way of telling where the scribes were intentional vs sloppy.