Hmm.... judging from this, this kinda happened when the rest of the battleships are still in the candidacy at middle school (with both Nagato and Mutsu starting to gain their assets) and Admibro was out seeking the wayward shipgirls. he first found her and of all the shipgirls she's the first to gain her combat rigging as the candidates are still there in the dorms at this time.
I suspect the girls at the candidate program had seen Admibro with long hair which in the long run solidified their affections for him.
oldies that are most likely with him here are the CV Houshou, the Fusou and Ise class BB's as well as the second flagship of the Japanese Navy Mikasa.
Hmm.... judging from this, this kinda happened when the rest of the battleships are still in the candidacy at middle school (with both Nagato and Mutsu starting to gain their assets) and Admibro was out seeking the wayward shipgirls. he first found her and of all the shipgirls she's the first to gain her combat rigging as the candidates are still there in the dorms at this time.
I'm inclined to think this is just the recruitment into the shipgirls program. Admibro here has his own sixth sense that helps him figure out what ship a candidate has the greatest affinity for, but actually becoming a shipgirl will still require transferring to the shipgirl academy and going through the training program.
(Of course, it doesn't have to be Admibro who identifies the candidates - perhaps he is just the one going out to do the recruiting. But if shipgirl candidates have the paranormal ability to see fairies, then it could also be that admiral candidates have a similar paranormal ability to relate to shipgirls or shipgirl candidates, and to sense which ship-spirit would be their best match.)
In any case, this might explain how Kongou was so sure of herself. If a young long-haired Admibro told her "You are Kongou" as definitively as he told this girl that she was Ooi, she might just have been impressionable enough to be swayed by such a charismatic declaration.
In short, I would say that Ooi was one of the first girls Admibro recruited, as shown here; the recruitment of other girls is yet to come.
I used to ask around in regards to No Data Ooi, and a japanese friend told me about the early days of Kancolle. Beta testers of Kancolle started out with Ooi instead of the first five, and that might had ended up as No Data for the full release of the game