GE: scores are added together for a possible total of 40. When a double panel is used the averages of each pair are added together.
Visual: proficiency, analysis, and guard are added then halved for a possible total of 30.
Music: brass, analysis, and percussion are added together and halved for a possible total of 30. When two drum judges are used their average is used as a single perc score.
GE + Visual + Music = Total
40 + 30 + 30 = 100
It looks to me like the smaller panels early season tabulate by adding whatever they have in each caption together then using an appropriate multiplier to get the same ge, vis, mus weighting. 20+20 = 40 x .75 to get 30 with two visual judges, for example. Could be wrong on that, I haven't retabulated a lot of early season recaps.