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The bonus wagering playthroughs in the database have usually somewhere between hundred up to a thousand spins per slot. If you look at that number of spins, you will see RTP and it can differ lot from what official value says, and it is statistically normal for that period. For example, a slot that is certified to a 96 percent RTP may give 45 percent or sometimes even 135 percent in 500 spins just because of random mathematical variance.

To get a real reliable test of RTP you need at least ten thousand spins per slot - and more than hundred thousand spins is better. The bonus tests here focus more on short-term results and unique ways casinos pick slot configurations instead of showing the exact long-term RTP. Take the data provided as extra info, not as a ruling on slot quality.