By the same tokens, that could preclude insistence upon the equivocation "Mother of God".
If those in attendance at Council of Ephesus had intended to convey fullest sense of the term 'Mother of God' they could have (and would have?) coined a phrase conveying more precisely that very sense, yet they did not. They refrained from going *quite* that far with things, at that time...
It was only later individuals more commonly began further elevation of "Mary" towards being über-saint, the highest of all those perceived to be saints.
That papyrus 470 has possible early date (AD 250) is rather slim chance [see Dating the Sub Tuum Praesidium – Is Marian Veneration Apostolic? in ending note concludes;
Furthermore, regardless of whether it is third or fourth century, it is the first such example of prayer to Mary. From this, we can reasonable infer that prayer to Mary is not an apostolic tradition – it is a human tradition that arose centuries after Christ’s resurrection.
I much prefer “God-bearer” and “Theotokos.”
While I would say that “apostolic tradition” and “[merely or simply] human tradition” do not exhaust the possibilities, I do get fretful at the excessive claims of my co-religionists. I think it's a fine prayer. It's clearly an old prayer. I don't need it to be from the Didache or earlier. And, just as you say, third century ain't apostolic.
My go-to brief Marian prayer is coming up on 200 years old. My favorite longer Marian prayer is not 1k years old. Though I'm grateful for the clarifications and titles of Ephesus and Chalcedon, I haven't based my decision about the intercession of the saints or which prayers I like on their age. I hope you are well.