Yeah, but even if we use the definition of NTR that they use for the tag at the vndb, BB fits pretty well.
Netorare (寝取られ) is a sexual fetish designed to cause sexual jealousy by way of having the heroine indulge in sexual activity with someone other than the protagonist.
For a game to be classified as Netorare the following conditions must be met:
1. The heroine either must be romantically involved with the protagonist, a potential romance for him or of someone that the protagonist shares such a close relationship (sister, mother, osananajimi etc.) that jealousy is a factor.
2. Related sexual events are explicitly shown to the player or later described in detail.
This does not include relationships of heroines that are outside the route you follow. Explanation: Route 1 is for Heroine A, the protagonist is romantically involved with her. During that route, if she sleeps with other characters than the protagonist, it would be NTR. But during Route 2, which is about Heroine B, where the protagonist has no romantic relationship with Heroine A, her having sex with others wouldn't count as NTR.
If we look at point #1 BB fits the set up like a glove. All the ladies in the game are not only potential "romances" for Max, they are also related to him. All the scenes with Eric and the girls are meant to inspire jealousy in the player. So the stuff with Ann and Kira absolutely fits because you see all of the sex is SHOWN to you. Kira specifically is
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she starts off being blackmailed then comes to enjoy it (or can, anyway)
The only reason that the Alice stuff wouldn't be NTR is because the sex happens behind closed doors and was not actually implemented with images, though we know it happens, the stuff with Lisa as well, though as it stands when the idea was dropped, there is at least plausible deniability that nothing really happened.
But you are right, even if you don't want to call it netorare, the stuff with Eric provides the exact same emotional response in the people who hate it.