I've looked at those not listed on the PoW database and found:
Appleton, Lamb, O'Donnell, Phillips, Pocock, Poynter, Rourke, Smith 9019, Thompson, Wall and Walker 921 where all killed and so where probably never PoWs. With the exception of Smith and Thompson all are commemorated on memorials to the missing.
Bass, Berry, Darville, Foster, Hill 2529, Leaver, Metcalfe, Morrison, Ryan and Walker 921 are not listed by the ICRC or CWGC. A Berry F is listed by the ICRC but with no connection to the Manchesters - PA 359.
Mangin is 2528 Morgan
Shelsher could be Schelster - any thoughts appreciated. (PA414).
Walencting - I'm at a complete loss with, I've tried Valentine and a few other names that came to mind but with no luck.