Having not dis-assembled Exdos [2.0] yet

No need for disassembly, we have the source! But 1.4 is the current "best" version - it is the original 1985 1.3 with various improvements by Zozosoft. Version 2.0 is an original 1985 version produced for a 6MHz Z80 prototype that never saw the light of day and does not have the improvements. Version 3.0 is in the pipeline but currenly stalled due to lack of time in life!

I note that the original bus extender provided address/position coding. so a card in pos.1 has rom in segment/page 10 using ports 10h - 1Fh,  pos 2, rom @ 20, using ports 20h - 2Fh   etc

You are correct, but that address/position decoding is not used by anything - that capability got "lost" in the transfer to Hungary so all cards are fixed (or have config switches). The EXDOS software expects the EXDOS card to be fixed at the 10h-1fh range

my question is : Does Exdos actualy use all 16 ports in its allocated renge?
i'm guessing that n0-3 are the 1770 controller (duplicated @ n4-7) and n8 - nFh are drive signals duplicated 7 times. I would lile to have 2  of those ports avai;able for extra options.

During data transfer the EXDOS software points register C to 18h to look at the drive/WD1770 signals and uses DEC C to point at 17h - the "reflected" WD1770 data register - as the only way a 4MHz z80 can do it quickly enough. At other times it accesses the WD registers at 10h-13h as you would expect. But I don't *think* it ever accesses 19-1fh but I can't swear on that!

A couple of different types of overclocked "turbo" exdos cards were subsequently made and they use port 20h to control the overclocking.