Thank you so much for all your trouble! I had noticed that this William Smith had become a Chemical Labourer by 1871, living with Esther in Floodgate Street, but I had missed the possible connection between the cousin, Caroline Taylor and the Mary Ann Taylor witness on the marriage certificate. You are right, that could possibly prove to be very significant! What still troubles me is that I cannot find, as yet, a census entrant for a 5-6 year old Hannah on the 1851 census anywhere in Warwickshire that fits with the facts I have. I will try to find her GRO birth registration.
Thank you again!