I agree about the search range for DOBs. I chose the range for the earliest dates because I didn't read your complete msg. Suggest you choose a more suitable range and try it.
On using Griffith's Valuation, this survey's intent was to gather info for property taxation. It identifies only property owners or leasors and lists the property holder's name without stating an age, or other giving the identity of other persons. Thus, it totally excludes the largely landless peasantry. The same individual could be listed multiple times if he/she held multiple plots. Its only merit is that all census rcds prior to 1901 were destroyed by accident or design.