Alright, so what is with the monthly scores, then?
In original, when I am fully inactive, I get these.
Number of UFOs spotted in January across 3 games: 4, 5, 4 + 1 terror site in each game
Scores: -1100, -1117, -1117
The value of -1000 and a fluctuation of -100/200 in January is consistent across all games (about 20-ish now).
In Open Xcom, number of UFOs: 3, 2, 4 + 1 terror site in each game
Scores: -854, -843, -844.
Again, the number -800 and -50/100 is consistent.
Veteran difficulty in both cases.