Shevliaskovic and Tim are both right I just want to point something very important about how chords work in general. Because we build chords in thirds and we consider triads (3 note chords) to be the basic unit of a chord, the more notes you have the more triads you can break them into.
For example the E♭Maj7 is spelled:
E♭ G B♭ D
We can make two different basic triads out of this which are:
- E♭ major (E♭, G, B♭)
- G minor (G, B♭, D)
These both are the basic building block of the you noted the chords (Gm(add♭13) and E♭Maj7) can be considered when naming a chord. Depending on what key you are in, where you are going, and where you are coming from one name will make more sense then the other.
As a result of the added tone you can see that both a major and minor triad can be derived and the resulting chord will reflect that whether you call it a major chord or a minor chord. As your chord get bigger in general you add "color" to the sound and the resulting sound is a combination of the sounds not just one or the other.
Another good example of this is the dominant 7th which build off C is:
C E G B♭
We can make two different basic triads out of this which are:
- C major (C, E, G)
- E diminished (E, G, B♭)
In this chord we don't just want the typical major chord, we want the dissonance that diminished chord brings, but at the same time we want to be more stable which is found in the major chord. So the chord quality blend in a way we take advantage of.