How can they be distinguished, then?
The Greek grammar shows how.
Kecharitomene is a Greek perfect, passive, participle, which could literally be translated "having been graced," since the root of the word is "charis", which means grace. Ephesians 1:6, which refers to Jesus Christ, uses the aorist, active, indicative echaritosen, meaning "he graced."
See the difference? Mary, passive voice, she received grace; Jesus, active voice, "He graced." This is due to the fact that Jesus is a Divine person; Mary is a human person, a creature and handmaid.
In Luke 1:28 "Kecharitomene" is nominative or titular, since it follows the greeting "Chaire" ---"Hail [name or title] --- thus the name would automatically be capitalized in English translations.
The unique feature of Kecharitomene is that it is in the Greek perfect tense, denoting that the state of grace began in past time, by a completed action (hence "fully" accomplished), whose results continue in the present. A suitable translation to denote all these features might be "Fully-Graced One." The Greek passive voice denotes that Mary received the title from an outside source, in this case, ALmighty God.
The New Testament uses the Greek "pleres charitos" ("full of grace") to describe Jesus (John 1:14) and Stephen (Acts 6:8), but these usages are not as specific to time, agent and continuity as Kecharitomene.
Like all of the name changes in the Bible, it indicates the person's status as seen by God, the person's predestined giftedness in order to be equipped to play their role in God's plan:
It's the only place in the Bible --- the only place in all of Greek literature ---where this word is used as a form of address. It's unique. It doesn't make her equal to God (passive voice: it's been done unto her) and not identical to what's said of Stephen, because it's
This unique neologism Kecharitomene is the best Greek word that could have been invented by Divine inspiration to indicate Mary's sinlessness, her being equipped to play her role as the natural source of Christ's human nature, His flesh: human, yet untainted by sin. No other Greek formulation could have conveyed it all.
None of that proves that Mary was immaculately conceived. It only shows that Mary was full of grace at the time the angel spoke to her. Trying to extend that “full of grace” back to her conception is simply a man made concept.