Much love to you, OP.
Not my own experience, but my son's. I had PCOS so badly I was told it was a million to one chance I'd ever conceive. Tried for baby for 8 years - with no luck. Gave up on the whole idea and went to college.
Then I was suddenly pregnant! Brilliant. At 12 weeks, I had a devastating miscarriage - not my first and I had another one years later but this was truly horrendous.
So I went about my life, sad but resigned to the reality we'd never have kids.
Two months later, I felt something move...
Turned out I'd been expecting non identical twins and although one had died at 12 weeks, the other went to full term.
He has said, occasionally, he always felt something (someone) was missing from his life, and he was quite a solemn little baby and toddler (now 26!) Even just a year ago or so, he said the same thing.
I had a lot of subfertility treatment to get No 2, three years later and I maybe thought once or twice he wouldn't be here now if No 1's twin had lived. I think it's fairly obvious with twins, I'd never have actively sought out treatment to get No 2. But you know what? It's many years since I had that thought or even cared about it. He's here so he was meant to be here. The baby I lost is still a reality to my husband and self and even his twin - but no-one else. As time passes, it becomes just part of your reality and there is no way any one child supplants another, anyway.
No 2 turned out to have atypical autism and I just comforted myself thinking we were meant to have him because we could give him the great life and lots of love, he needed. In my objective mind, though, I understand No 2 did not really come to me because I lost one of my twins. The two things are unrelated.