Thanks for your suggestions ColC.
Dealing first with the William and Sarah marriage, I agree that it is around the right time - and as far as I can see, Ombersley is not too far from Upton Snodsbury and North Piddle, where James and Sarah are subsequently found. That said, there appear to be a few oddities - no least the fact that with a marriage in Nov 1812, it seems odd that William & Sarah's first child does not appear to be baptised until Dec 1819 in Ombersley - unless, of course, the other baptisms mentioned earlier (Ann & Eliza in Jan 1813, and Mary in Dec 1818 - all in Pershore Holy Cross) are also to this couple - and that they moved about a bit, locally. There is also the baptism of Samuel in Jan 1821, again at Pershore.
All of these 7 baptisms could be to the same couple - looking at the dates - but it does seem a little unlikely that they would move back and forth between Ombersley and Pershore to this extent (but nothing is impossible of course!)
But there is also the changing profession bricklayer, mason and labourer. Again, whilst all could be correct, I have my doubts. Unless I can unearth some firm information on this point (such as possibly finding William's will), I think I'll have to proceed on the basis that the William & Sarah in Ombersley are a different couple to the William & Sarah in Pershore.
With regards to Samuel Davis's marriage to Deliah (or Delilah) Ewins in 1867, yes I have various pieces of information on that marriage (which was by license - marriage date Dec 26th 1867), and the children of that union (Emma E Davis in abt 1870 at Abbots Morton; Samuel Davis in abt 1873, also at Abbots Morton; and Ernest James Davis in abt 1874, at Alcester, Warwickshire). Sadly, Deliah then died in March 1875, and Samuel senior does not appear to have been able to keep any of his children with him - as I've found them all 'farmed out' with friends and relatives in later censuses.
Samuel senior (my great grandfather) seems to me a bit of a rascal - as I think I next find him marrying a Mary Jane Bott in Stafford on 26th August 1879 - claiming to be a bachelor! I accept this could be a completely different Samuel, but other facts I have (that I won't go into here, unless requested), lead me to the view that this is indeed the same Samuel who had earlier been widowed, by the death of Deliah. With Mary Jane he had 2 more children (Arthur & Gwendoline - I've got the dates somewhere but can't put my hand on them just now) - and then his second wife, Mary Jane died in Uttoxeter in December 1885. It is from Samuel's 3rd marriage - to Maria Heywood, formerly Shaw (a widow) - on 16th July 1892 - that I am descended.
Samuel seemed to be extremely coy about his age/date of birth, which varied considerably over the course of the various censuses, and also on each of his marriage certificates! He died in Uttoxeter on 11th July 1918, with his death certificate recording his age as 64. As you will have gathered, I have my doubts as to the veracity of this!
Anyway, I realise I've rambled a bit here - but hopefully it adds a bit of interest to those of you who are kindly lending your assistance with my problems.