I was thinking the statement, “full of grace,” was a description rather than a title.
But that aside, I believe Mary’s being filled with grace was indeed different from the way other saints were so filled. As you said, she was from birth so filled. Yet other saints did not become filled until much longer after their births. Reminds me of something I once heard a pastor say: “We are all leaky vessels.” While saints can become filled, their sin creates a kind of leaking so that when they sin they are no longer filled–at least not fully.
So one might say to Mary, “Hail Mary, who always was filled, is filled now and ever will be filled, The Lord is with thee.” Or if we do not say such words, perhaps this understanding of them will come to mind when we do.