Well, an example of 'first person better informed' would be Darley's first two volumes of THE AXEXANDRIA QUARTET (ie JUSTINE and BALTHAZAR). When he got more information about what had been going on, he retold the story incorporating it.

Iirc the third volume, without Darley as narrator, just a conventional third person voice, was regular omni.

At the moment I can't think of a good example of first person omni (ie all told looking back from the very end point) though I'm sure there are some.

I think it's a useful distinction, but there are a lot of points along that continuum.