If the frames that are fine were only in the position for exposure for a short time, then they might not have been affected by a light leak. If, for instance, you shot three in a row fairly quickly, the middle one may not have been in the spot where it would have been leaked on for as long as the other two frames.
The frames you attached do look like a leak to me and one that could be from the side seal of the back rather than the middle or top/bottom somewhere.
The light leaks could be a different issue than the unexposed frames. Were the frames that came out in the same amount of light as the ones that didn't?