That could well be - from Shakespeare's point of view, though, Miranda
was just another gerundive of obligation! Just as Perdita
was just another past participle, and Marina
was just an adjective. And educated parents would have been able to do what he did, in the Middle Ages or whenever, if they liked. The difference is that, if a girl was to be named Amand, then the one making the change to Amanda
would have been the priest; and he would have been writing down a feminine form, not a gerundive with its own meaning.