It's hard to tell sometimes when an alter is new, re-surfacing, or just new to your awareness. I thought I knew everyone when I knew about 4 of my alters (including the original core). There was Kat, Rain, L.C., and Cassie. Then I learned about one more alter and I was aware of 5 for awhile. Then I learned about another, so that made 6, and then another, so that made 7, and then I learned about 2 more after that for a total of 10! One of them, "Hannibal", is good at hiding, so that's why I didn't realize he existed until later on. 2 of them, Kyra and Rebel, are re-surfacing ones, one of which I didn't realize I even had. One, Ray, didn't start to noticeably show up until later and it was hard to learn about her since she came and went so quickly, so that's why I didn't learn about her earlier on. And the other, Lynn, I'm still not sure about, because she seems to be a new split off of Cassie but at the same time she could simply be one that I was never aware of.
I can't feel the presence of "Hannibal", Kyra, or Rebel, and so far they've only come out when triggered. I can't "see" them, I can't hear them, and I don't think they can hear me or anyone else. Though I've learned where Kyra and Rebel come from, no one in my system knows where "Hannibal" came from, or much about him (hence why he doesn't even have a real name). I "lose time" when any of them come "out".
With Lynn, I'm aware of her but I still lose time when she comes "out", and so far I'm not able to consciously switch with her yet, so she also only comes out when triggered. She came into my awareness after I moved from my apartment into a house with roommates, and I was feeling very cramped and uncomfortable since I was used to living by myself. I just wanted to go home, and that's all she ever seems to want. So I'm not sure if she was created due to that period of time, or if she was always there and was just triggered into awareness due to that period of time.
I'm sure this is of no help to you, but I wanted to at least let you know that you're not alone in your wonders or questions.
If you're able to, try talking to them, or even writing a note, or if you have others that you're able to talk to, see if they can talk to them. Try to find out more about them, perhaps how old they are, and if they know, how long they've been around. Sometimes age can help you get an idea for how long they've been around as well. Cassie's 8 even though I split from her at age 10, mainly because she's afraid of being 10 "again", but also because she simply has more of an 8-yr-old mindset and needs. L.C. used to be 13 because that's when she came into existence. Ray is 10 because she doesn't know exactly how old she is, but she's been around since the body was 10 so she's been around for 10 years. So age might help to give you an idea of how long they've been around. But it's different with each system, so take that idea with a grain of salt.
On a side note, I certainly hope that your boyfriend is better and that you and your little girl are safe. I also hope that in case he should go through that period again, you're able to keep yourself and your little girl safe and have saftey plans, such as numbers to call and places to go in case your safety's at risk as it seems it was before.
It just occurred to me, does it really matter if an alter is new or simply new to your main group? Either way they're new in one sense or another. Even those in your main group were new to you at some point in time, so other new ones shouldn't be treated any differently. I can understand curiosity about if they're new or simply new to your awareness, but it doesn't really change how you "handle" them, I guess is what I'm trying to say. Try to learn more about them, try to help them with their unmet needs, and try to accept them as part of you just like any others you already know about (your main group). If it's possible, help them to become part of your main group so that you may all work together as a functioning system. I wish you the best of luck with this, and hope that you're able to receive more helpful advice than I was able to give. But at least know that you're not alone in having new alters, whether they're new or simply new to your awareness.