Volutar's here.
First of all XCOMFan419, welcome!
Second of all, you are misunderstanding nature of geo1/2 switching in the original xcom.
Fact#1: Geo1 is always the track which NEW game is beginning with.
Fact#2: Current track number is kept in the save file. So if you were listening for geo2 before saving, you'll get it after loading.
Fact#3: Geo1/2 switch happens ONLY after mission debriefing (battlescape end). No other ways to get track switch. And they are going one after another.
Fact#4: Interception music simply makes previous track reinit (play from the start).
In the OpenXcom, tho, we have geo tracks simply picked by random, and possibly switched after interception or memorial window. Last music played isn't kept in the savegame, and geo1 is always the one you hear from the beginning anyways.
All tracks from XCOM1 are looped extept for: Intro (all 3 parts), Win, Story, Lose.
There's no such thing as "geo1 finished, start play geo2" in vanilla. If you're old XCOM fan, you should know that.
It is possible to switch geo music after it ends, but it will sound really ugly, since they are not meant to be transitioned one to another, even through the pause.