I think you have your terminology mixed up a bit but I believe what your referring to is a 1/2 track stereo tape format standard versus a 1/4 track stereo format.
The first one uses the entire width of the tape to lay down the two channels of sound at fairly hot levels, (320nwb/m), and the second uses half the tape to lay down two tracks and then expects the tape to be flipped and used on its B side to record the next stereo pair of tracks at reduced levels, (180-250 nwb/m), so as to reduce the effects of bleed through and distortion.
I think you have your terminology mixed up a bit but I believe what your referring to is a 1/2 track stereo tape format standard versus a 1/4 track stereo format.
The BR20 is/was available in three flavours: BR20N, BR20D and BR20T.
The 'T' model has a centre timecode track. The other two are NAB and DIN, which I'm pretty sure have the same heads (as each other). I assumed they were the NAB and IEC versions, but I could be wrong.
I don't believe it's the track width. The NAB version was cheaper than the DIN version by several hundred pounds, though.
*EDIT*
Looks like I was wrong about the NAB and DIN heads being the same. According to some Tascam 32 literature I just found online, NAB has 2mm wide tracks, and DIN has 2.7mm tracks.
I wonder what the heads on my '32 were set for? Or are they different given that I replaced one of them? Oops.