Well - in case anyone is interested I have worked out what happened. First I should mention that the Allies surrendered turn 6 following the loss of Moscow. This is why … I think! …
Allied Error No 1: Previous games R has focused all its forces into W Russia w/out any of the secondary strafes/attacks advanced by others, leaving 1 inf in each of Karelia and Caucasus. This game I varied from that because I knew what G was going to do (the danger of a solo game) and left the Karelia garrison there with the thought that would test the G Leningrad in force strategy. In fact it did the opposite by removing the counter-attack option, unless risking a 50% attack which would kill R if it failed. If everything had been in W Russia the chances of that counter being successful would have been approaching 100%.
Allied Error No 2: Despite G’s initial success against R, the capture of Moscow was brought about by J’s rampaging across central Asia and combining with G. J took India in turn 3 - they are getting better!  This is, for me so far, the biggest challenge for the Allies and one for which I do not yet have a solution, except to make SZ37 work, which relies on G not committing it’s bomber to Egypt (see below) or the UK’s 3 unit builds there each turn going to higher value units, which is a hard call  given everything else the UK has to do. Perhaps that’s what has to happen …? Central Asia is the key! But then so is the N Atlantic! And …!
Allied Error No 3: The R fighter attack on the G Baltic fleet looks good, but w/out a R fighter in Egypt G has a 90% chance of taking Egypt. Â The R Fighter brings it down to 60%, unless G commits its bomber, bringing it back to 90%. So nothing clear there, 'cos either the bomber goes to the UK B/ship (if G has no Baltic fleet) or to Egypt. Either way the UK loses all of its western hemisphere naval and Egypt in G1, provided G is sensible in Russia. So not really an error, but a debate with myself.
Allied Error No 4: Desperate to get US forces across the Atlantic I took risks which resulted in massive loss of US naval materiel as the cost of landing enough force to recapture Africa. Two huge battles in SZ13. More caution might have worked better?
Allied Error No 5: Too slow to get carriers off US east costs and UK of fighter reinforcements. The UK was simply having to save enough IPCs after India builds to be able to place a N Atlantic fleet with some chance of survival in one go. The US was trying to get to Africa, which (as above) now seems like the wrong call.
I am going to stop posting every game on the board now. My very sincere thanks to those who have taken the time to respond. Their thoughts and my post and review process have been a huge boost to my learning. I do hope I have demonstrated that learning in these posts. But I think I have already drawn too much on your generosity and helpfulness.
Thanks again everyone.