There is an extensive comparison over here
http://gamemusicfreak.blogspot.com/2...ial-discs.html
It might have just been a mistake they left the real catalog number there, also note the "Made in Japan" on the back.
Unless it mentions "Licensed by Falcom", I doubt that it's legit. SM-39 is Music from Ys I and might be the first game music CD SonMay published.
The year is not earlier than 1991, though.