Here's the thread from last year when I reported my Savannah Cherry (e. calycina) fruiting solo:
https://tropicalfruitforum.com/index.php?topic=51078.0. K-Rimes suggested it might be a COTRG + Calycina hybrid. I don't know enough about them to tell. Last year my COTRG wasn't yet flowering, the only Eugenias I had flowering were uniflora, pitangatuba, and this calycina.
The seeds from these fruit all sprouted, though I threw most of them away as this is a common variety.
It is fruiting again right now with many fruitlets and some mature fruits already, and while this year I have been cross-pollinating all the eugenia flowers that are blooming at the same time this is still the only mature calycina, the rest are COTRG, uniflora, or others