Potentials are bugged?...

So basically I've seen some odd (and rare) cases of like B- or C+ having 85+ potential (if you go on edit to see their real potential), while some B+ don't reach those values.

And then another case, for example Ibaka from Oklahoma, has 75 rating, B- potential, but when you go on edit it says 70 potential... how come he has 75 rating and 70 potential? Overachiever at age of 22? lol...

Now I'm wondering, is this a bug? And what really counts, the potential (B-, B ,etc) or what is stated on the edit function?

I don't think potential is meant to tell you what their best overall rating will be, but how much they will improve on their current rating.
Ex: a 67 overall with 90 potential will be better than a 70 overall with 65 potential (assuming they are the same age)

The problem with the grades not matching the number rating is most likely just a bug.

I made a quick research which came out with interesting results...

Basically potential seems dynamic.

From season to season, I saw Mcgee evolving not only his overall but also his potential, from 79 to 83 to 85. His overall peeked at 82 and stoped.
Crawford started 67 overall with 76 potential, he went on to be a 80+ overall with 85 potential.
Ibaka was 75 overall with 70 potential, evolved marginally to a 77 overall with 71 potential, then started to drop stats at like 26 years old.
Kevin Love, 81 overall 82 potential, became 83 overall 83 potential. Pretty much didn't evolve afterwards.

In general I see a corelation between the potential (in edit mode) and the potential rating. So it does seem that the potential is never really a fixed value, but varies with time. The odd cases must be a bug indeed.

Also seems like potential, as you said, tells you more about how much the player evolves and not so much about the "rating cap". However, players with a potential that is equal or worse than your current ability seems to handicap your player in progression as seen by Kevin and Ibaka.
Players with much better potential than overall seem to have a much more steady and reliable progression as seen by Crawford and Mcgee, specially because the overall grows with the potential, meaning the overall-potential gap stays positive.

That's usually the way potential ratings work in both NBA 2K and NBA Live. I don't think there's actually a bug here, certain players are more likely to reach greater heights but potential isn't always realised...just a in real life.