Yes, Morrissania (168th) and 183rd St. (no name other than 183rd) were discontinued when the first hi-level platforms were put in. And yes, Claremont Parkway (172nd) had been discontinued way back in the 50s sometime. Remnants of all 3 are visible from trains today if you take a good look.
RE Wakefield: there is a checkered tale about the survival of this one. It was destroyed by fire in the early 50s, following which NYC applied to the NY State Public Svc. Commission (a tough-as-nails regulatory agency) to discontinue the station, this on the grounds that it is so close to Mt. Vernon. (Hey folks, you can easily see between the two stations, and it only a short walk between them). But, the PSC, whose policy appears to have been "whatever you want, the answer is no, period" required NYC to reconstruct the station.
Oh, one other thing, while on the subject of ex-stations, don't forget the 3 in the Park Ave. tunnel which I believe were closed when the Lexington Ave. subway went in a block away. Remnants of those are visible today too