Is it correct in this sheet that "A MI 7" means minor 7th (m7), "C MA 7" means major 7th (maj7) and just "C 7" means the dominant 7th?
It is as you say. A "MI7" is a minor seventh and a "MA7" is a major seventh.
There are several different labels in general use, so I'm putting them in this answer:
m7, -7, mi7, MI7, MIN7, min7 are all minor seventh names.
M7, MA7, MAJ7, maj7 and a small triangle are all major seventh names.
7 and dom7 are dominant seventh names.
MI is minor and
MA is major.
It is kind of funny compared to solfege where
MI is the mediant the major scale and
MA is the mediant in minor! I doubt that would really confuse anyone, but after getting solfege into my head, I can't help notice the opposites.
Keep in mind that the
MI/MA immediately after the root letter refers to the third of the basic triad. Interval numbers
9 by default are perfect fifth, major sixth, minor seventh, major ninth. So...
C minor triad with
(MA7) meaning add a major seventh for
C E♭ G B♮.
C minor triad - not
MI6 for a minor sixth - the sixth by default is a major sixth.
C E♭ G A♮.
When the interval numbers are modified they often go into parenthesis for readability, like `7(♭5)