The
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is a great place to check event requirements if you missed any.
The missable Ami events are all from either not pursuing her or not having enough lust. With Futaba you just need high enough lust but there is one event in particular that is easy to miss because it requires Makoto to have high lust after shes been unavailable for a really long time.
To see Tsukasa's events you have to both stay with chinami in the bath in an earlier event and choose tsukasa during the tutoring event. If you're worried about depraved options, you'll be more comfortable missing those.