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The first is a warning to not be complacient until your opponent's king is pushing up dasies--an extra queen and rook needed to make just one more defensive move. Second is my first smother in several years. The 3rd is trying too hard to win against a bad bishop which could defend everything necessary. Fourth is a successful rook sac.
Ouch. There are many mistakes in all the games.
For the third one, I wondered, but I think there is a way to win. Starting from the position of move 45, White plays the following steps :
1- place the knight on g3 when the white king can go out to the queenside and the black king is not on h4. The black king is then cut by the h5/g5 squares.
2- Bring the white king to the queenside, to b6 if possible, to a5 otherwise.
3a- If Black has kept his king on the kingside, play Kc7 and enjoy the free pawns.
3b- (more likely) If Black has brought his king to defence, try to provoke the advance of Black's h-pawn via Nh5-f6. The problem is that the bishop can cover the entrance square (h5) but there might be ways around (he must also defend the queenside against the next a4 and b5 plan).
As soon as this is done (or failed), play a4, Ng3-e2-c3 if the h pawn has advanced, and push b5. the end position after the trades should be the diagram below, which is lost for Black because of the zugzwang. If the h pawn has not advanced, a similar position (same pawn placement on the queenside) should be possible to obtain without trading the minor pieces, in which case it is easier to win.