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Does this alter anything?

Hell ya ! You don't have half the problems I thought you had ! The rear is going to spin when engine is cold simply from "Oil-drag". Bet it stops when the bike is up to temperature ! NOT an issue !

Not sure if this was covered in any previous comments, but I'd also check the left side actuator bracket under the cover on the lower cable adjuster?

Mine was pretty worn / distorted, and when I replaced it with a heavy-duty version, I was surprised at how small the retaining stud / nut (pushrod) and single-D (or double-D, can't remember) plate profile were.
if you have any wear / play in that D profile hole, or a loose retaining nut, that may eat-up effective travel on the cable and mislead..

I have managed to adjust clutch so changing gear is near perfect even getting back to neutral at any point hot or cold engine- but to do this with all the tweaks, the handlebar lever only bites at the point of releasing the lever so no clutch control and top cable adjuster wound in totally, I did try to loosen ( wound in) at bottom adjuster to give more play at top but then gear changing gets worst, unless the cable has stretched but looks good, bike only done 15k. Ps no slippage or drag either

Something's not right. At this point I would ask you to post a few pictures of the clutch lever pulled in and of the clutch actuator at rest and also pulled in. Something is out of wack.
It really doesn't matter whether the slack in the cable is adjusted out at the top of the cable or the bottom. All you're adjusting is the length of the outer cable to the inner cable. It's advisable to have some adjustability at the handle bar so that you can adjust it without tools if needed while out on the road.
What is critical is the relationship of the actuator lever arm to the cable down in the left cover. If something is out of wack, that lever will not be at the proper angle to the cable and the effective motion of the clutch actuator will be diminished and messing things up.
Things that can happen-
Clutch was allowed to be run while the clutch actuating rod was dragging and that will shorten the rod then after adjusting the clutch actuator is not in the right position as related to the clutch cable to give the proper movement. Ideally the clutch actuator angle to the clutch cable should be about 75 to 80 degrees before pulling in the cable. This will give the maximum actuator travel for clutch cable movement.
The clutch lever may have been replaced with a lever that doesn't have the proper throw. This may have been done to give a lighter pull on the clutch lever if the previous owner didn't have the strength in his left hand. ( Seen this before)
The clutch cable was replaced with a cable that is not the proper length. This will mess up the adjuster settings and you may never get the cable adjusted right.
Another issue that occurs is the routing of the cable from the handlebar to the actuator. If it hasn't been routed properly, the "feel" of the clutch lever may indicate something at completely wrong to what's really happening.
When you're doing all this adjusting, is the bike up on the center stand with the handlebars straight ahead or are the bars turned to one side or the other?
Are the cable ends seated nicely in the bottom of the adjusters or are they cocked on an angle in the cable adjusters? Sometimes the routing of the cable will cause the cable to sit cocked up in the adjusters making it impossible to "get the adjustment right"

If after checking all this out and you're still having clutch drag problems, then you need to check the ears on the clutch basket for chatter marks. You say the bike has only 15K on it. That may be what the clock says and maybe someone wound the clock to read that. I trust no one when it comes to mileage. It's too easy to wind the clock back and a 35 year old bike with only 15 K ?? That's a stretch. Hell, I could do 15 K on a 2 week vacation. My buddy went from Toronto Ontario the Vancouver BC, then down to Yuma Arazona then across to Tampa Florida and back home in 9 days. That trip was 14,568 KM. We call it the "Iron Butt Run"

Some contradictions in your approach are confusing.
I have managed to adjust clutch so changing gear is near perfect even getting back to neutral at any point hot or cold engine-
This is good !
but to do this with all the tweaks, the handlebar lever only bites at the point of releasing the lever so no clutch control and top cable adjuster wound in totally,
This is not good or normal
I did try to loosen ( wound in) at bottom adjuster to give more play at top but then gear changing gets worst,
Turning either adjuster IN effectively lengthens the cable requiring MORE lever action to disengage the clutch. This explains why you state <the handlebar lever only bites at the point of releasing the lever>
unless the cable has stretched but looks good, bike only done 15k. Ps no slippage or drag either
The "Stretch" will be minimal. The adjusters deal with this.
KB's point about an after-market clutch-lever is VERY valid. Had this problem and had to go back to the OEM lever.

Thanks for the info, if only I could do that mileage ,,, had the bike about 3 + years had nothing but problems with it, trying to get through them & all down to you guys, if I said I average about 100- 150 miles a year it's a ongoing joke, finally getting somewhere now runs without breaking down, starts with choke properly and can leave over a period of time and will start ok, just had relay fitted due to overcharging ,
Friday booked to go away to the coast with a pal for weekend & only 200m round trip biggest ever. I have had about 30 + bikes & I have to say this one the biggest challenge yet. Back to clutch it has totally failed now somehow! Last night I went for a lovely 30 m run everything worked could get into all gears and even neutral, but no clutch control at top hand lever , near when lever being released, bottom clutch lever 90 degree to cable, top adjuster hardly adjusted bottom fully to pull lever to 90degree. I decided to tweak today and presto clutch won't work at all now, I rode back into my garage last night all ok, now put into gear and doesn't matter how many times I adjust it all I cannot disengage the drive to back wheel with clutch lever pulled in, in neutral wheel disengaged. Perhaps I have done something on the 30m run like worn the rod? So much for my intended 300m this year ! I didn't take any pics before I wrecked it sorry