I think Burnham was referencing Book, not Tyler, when she said she knows what it’s like to lose someone but got him back.
I suppose you could interpret it that way, but I just don’t see it myself.
Book died during the final events of 10C, but they magically zapped him back into existence, if I recall correctly.
Book didn’t die, he was transporting out, and the 10C were able to capture his transporter pattern, and then later resolve it.
Not surprised there wasn’t a close-up on that one; I wouldn’t have recalled that Janeway has a microscope in her ready room.