Matches in our historical database, counted from the live data files on every deploy. API = structured results with scores and stable team ids; Betfair = results reconstructed from settled markets, so no scores; Tennis-data = tennis-data.co.uk archives with results, scores and closing odds; PandaScore = per-title esports match histories with map-level results, powering the dedicated CS2 and Dota 2 rating models. That difference is why some models are stronger than others, and we publish it rather than average it away.