I'm talking about true MSX computers, not MSX-ish, or partially compatible MSX computers (Spectravideo 318, I'm looking at you).
The first MSX, the Mitsubishi "ML-8000", was released on October 21st, 1983. Four days later, the second MSX, the Sanyo "MPC-10", was released.
As you mentioned, the earlier SpectreVideo claimed to be MSX, but wasn't:
The system most similar to the MSX was the Spectravideo SV-328 home computer (Spectravideo even claimed to be MSX compatible in advertisements before the actual launch of MSX systems, but it was in fact not completely compatible with the MSX).
I also feel it's worthwhile to include a picture of the first issue of MSX magazine (which for some reason features a cigar-smoking horse-man taking a bath in outer space):
Source (Japanese): http://weekly.ascii.jp/elem/000/000/179/179415/