When AFM Stereo was introduced to 8-mm video?

[DVtyro]

Many 8-mm tapes, especially early ones, have "P6" prefix. I wonder what does it mean?

EDIT: It seems P6 means NTSC, P5 means PAL. Why these prefixes? Record/play duration was different in NTSC vs PAL:

PAL play time ≈ NTSC play time × 0.7

So, a P6-120 ≈ P5-85. I guess this was the reason 8-mm was not as popular in Europe as in the U.S.