Originally, Seven of Nine was going to use her human name on Star Trek: Voyager

When Seven of Nine (Jeri Ryan) was first introduced to Star Trek: Voyager in season four, she was going to lose more than just her attachment to the Borg. In the DVD extras of season four of the series, Executive Producer Brannon Braga [via Screenrant] said that the writers had originally intended for Seven to go by a human name, possibly as a way for her to integrate more fully back into humanity. And though the name she used before she was assimilated was revealed, she never chose to utlize that name on Voyager.

As it turns out, it was decided that keeping Seven of Nine's designation set her apart from the crew and that was what was needed, considering she'd spent most of her life attached to the Borg. She had no real knowledge of her humanity so it made sense she'd choose to go by the only name she knew.

""We struggled for a long time. Initially, we gave her a Human name. She was gonna be named Pera, or Annika, or something. We wrote the first couple of scripts with a Human name. And it wasn't until a little later that we thought, 'She shouldn't have a Human name. She should be set apart, in some way.'""

- Brannon Braga

And even though Seven had integrated back into the human world by the time she met Admiral Jean-Luc Picard in Star Trek: Picard, she still chose to go by her Borg name. This was a bone of contention between her and Captain Shaw when she served aboard the USS Titan as his second in command. He referred to her as Commander Hansen and not Seven of Nine, but that was mainly because of the trauma he'd experienced at the hands of the Borg. It was only as he lay dying aboard the Titan that he acknowledged Seven for who she really was.

It was a poignant moment when he handed command of the ship over to her and called her Seven of Nine. In truth, Captain Shaw had known all along who she was, but in his final moments of life, he gave her the acknowledgment she'd been seeking from him. And that was just one reason why having her keep her Borg designation was the best decision.