The combo portions of stable's score V1 and score V2 differ in rate of progression. While score V1's combo portion is quadratic in progression in relation to current combo, score V2 is initially logarithmic until 200 combo, after which it is linear. This was demonstrated in prior work in #24823 and #24924, and is apparent on the screenshot below taken from catch's TestSceneScoring
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Notably, catch is the only ruleset wherein the rate of ascent differs between score V1 and score V2. This means, that for all other rulesets, it was completely fine to estimate the combo portion of score V2 / "standardised" scoring by just taking the linear ratio of combo score achieved on the beatmap to maximum combo score achievable on the beatmap.