NC21 clutch types query...

[harvey_s]

I have an '86 NC21 and the clutch was apparently not too good according to the guy I bought it off - but recently it started slipping quite noticeably so today I took it apart.
It had 10 x 3.0mm friction plates and the plain plates were pretty blue and quite thin at 1.5mm thick.
I did have a spare clutch pack from another NC21 and it looked pretty good with friction plates that measured up well within tolerance and nice shiny dimpled plain plates.
But although I used it and it seems OK on a quick spin up the road - it wasn't exactly the same...
Although the pack measured the same - this pack has only 9 friction plates and the plain plates are twice as thick at 3.0mm and the innermost friction plate has a much larger bore than the others (about half of the friction area).
Anyone else come across this?...and any idea why Honda put the odd half plate in?
Cheers