The L6a and L6b abbreviations are for two sublayers of L6. They have some differences in connectivity, but the functional organization is probably much more complicated. Sometimes cells with different connectivity patterns, properties, or whatnot aren’t physically separated into sublayers, which is true in L6.
L6 ip, mp, and bp are probably inverted pyramidal, multipolar, and bipolar, although I’m not sure. I don’t know if they have important differences. They might just be physically like that because they’re at the bottom of the cortex and development stuff, dunno.
Diagrams of the actual cortex are very complicated, so I wouldn’t pay too much attention to them for understanding numenta theories. They’re mostly about biological plausibility for numenta theories.