Ah, so it looks like you have a good bit of information on the next generation. Perhaps you even know if this 21 South Main St address ties to the later Shudall's shop at 68 South Main St.? What's this ledger - is it from a shop? Perhaps you know what became of this George junior? Perhaps you know the Mackey + Hogan connection? Neither name is common in Wexford so you may be able to trace that.
As for tracing the death the main thing to remember is that Shudall can be spelled in a lot of different ways depending on who was writing it down at the time. So I suspect her death was registered, but the spelling might make the search difficult. There is a 1937 death registration for a Mary Shudall but it shows her to have been born in 1840 so that can't be your g.grandmother; though I suspect this age of 97 is incorrect; so you could get that certificate to see if the residence at the time matches your line.
Do you know if anyone was left in Cullenstown after Thomas' 1923 death? And yes, the Shudalls were Protestant, but some of them changed to Catholicism. Those living are of both religions.
From what you say here, the main question is, how do you know this Mary (not Mac Evay) is Mary Mackay not Mary Shudall? I presume you have more information which I guess came from oral history? Perhaps you know Mary Shudall married someone else?
Meanwhile can you tell me the details on the Mary + Thomas marriage certificate?
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