David,
I also knew about the other Albert Clemens but, nevertheless, my facts are correct and that my great uncle (my father's uncle) is indeed the same Albert as your great grandfather. The age issue is not what it seems since my father was 44 when I was born (I'm 64 now) so I am not surprised that your father is in his 80s! I have a number of images relating to Albert each showing his part regimental number as 8470 and that he was in the Yorkshire Regiment. I also have the war record showing Albert (again 8470) as a Private when killed with the 6th Battalion of the Yorkshire Regiment on 21 Aug 15. It is very likely that when he re-enlisted, his previous service record of Sgt was taken into account and that at some point he received accelerated promotion from Private through to Coy Sgt Maj in a very short space of time on the basis of past service, maturity and, sadly, the heavy losses around him. The most likely reason he is listed as a Private in the war record, but in family memory and on the the Helles memorial as Coy Sgt Maj, is that his acting rank was never recorded as Substantive (or permanent). After a war, servicemen holding substantive rank often reverted to their former, substantive rank or sometimes maintained the rank after hostilities; in Albert`s case it simply meant that he never had such an opportunity and still held the rank of substantive Private when he was tragically killed. I am even more proud of him for that reason; he belongs to a very small group indeed that proved able to rise from Private to Coy Sgt Maj in less than a year and is listed as such on the Helles Memorial. Finally, did you know that his name is recorded on a church panel in St Nicolas' church Bolton Colliery where the Hackney Clemens's moved to? I also have a photo of my grandmother Francis Annie Frater (who married my grandfather Vernon, brother of your great grandfather Albert) with her sister, who I am told, may have married Albert. If that`s true, then the picture is of your great grandmother. Perhaps you may know about this – if she was called Frater before she was married then the link is true.
Best wishes
Phil