Just a few suggestions, as Google can't provide the answers.
GvI, if it means Glasgow versus Ireland, is obviously not a full international match for which caps would have been awarded to Glasgow players. They MAY have been awarded to the Irish players, though - and, coincidentally enough, the Irish team played in blue during 1921. So, maybe he played for Ireland but, as it was not a full international, it hasn't been listed in Gadget's book.
1921/22 was the year of Irish partition, and security was a huge concern. A 1921 Irish cup match replay was moved from Dublin to Belfast purportedly for that very reason. Possibly - only possibly - the match in question was also moved to Scotland for security reasons. In which case (although if this were true, I'd have expected the cap to say IvG) the G may not mean anywhere in Scotland at all, but rather an international team beginning with G.
Just food for thought.
Mike
EDIT: A further thought. It's only an assumption that Scotland is involved in any way. How about Germany v Ireland with the match being played in Germany (would that have happened, I wonder, so soon after the war?) Of course, then we'd have the problem of the non-inclusion in Gadget's book all over again.