I searched the forum and found some interesting information on how the ELO calc inouts are determined by the ELOs at the time the game finishes, for example in a long run in correspondence game. I also saw on the wiki the reference to the use of Glicko formula for ELO.

What I haven’t been able to see is how handicap plays into the system. For example if a game starts as even with two handicap but your opponent ends game having the same rating of you how are will ELO be calculated. Similarly if you win/lose in an unevenly handicap game how does that feed into the calculation?

If the threads talked about ELO, they are outdated. The name Glicko(2) is used when talking about the new (Aug '18) rating system. The informations in OGS Ratings Revisited are outdated (not how glicko2 and our rating algorithm works by any means).

1 stone handicap is worth 1 rank. Black’s rank is adjusted for rating calculation. The ratings used are always the recent ratings. It doesn’t matter if a game was fair at any time. The (adjusted) rating difference leads to a prediction of how probable a win is (again using recent ratings). If the win is expected, the rating adjustment is minor, if it’s unexpected it’s big.

So if I understand correctly the handicap stones are used to add/subtract to Black’s ELO in the glicko2 formula? Would be interesting to see a summary of the maths.

Glicko is hard to summarise. It uses multiple games for rating adjustment (batches of 15 games or 1 month, whatever is less; a full batch is closed and a new batch starts).
glicko2 math: http://glicko.net/glicko/glicko2.pdf

As a point of clarification in the event that you decide to dig deeper into how this rating algorithm uses, Elo is a specific rating system, not a generic term for rating points. So, if you start searching for terms about Elo points in the Glicko2 system, you’re going to have a much harder time getting specifically relevant results.

(It’s also worth noting that Elo is not an acronym, it’s the last name of Arpad Elo, the man who invented the system.)