Thanks for the careful and informed analysis. I want to weigh in here, very tentatively, on a minor point, one on which Rawleigh has commented, and on which I may (for the first and I hope the last time) differ from her.
I don't think Dennis signed his will O'Conry. I think he signed it Dennis Conry. I have the xerox of the microfilm copy of the will which Rawleigh kindly sent, and I can see how one could easily read the signature as Dennis O' Conry. Between the "Dennis" and the "Conry" appears a circular shape that can be read as the letter "O". But keep in mind that what we have is not the original of the will, but the transcription into the court records of the text of the will. Thus the "signature" is not his, but a copy of it by the clerk. And I have frequently seen such round characters as representations of a seal. In some cases, the clerk has attempted a sort of squiggly line to empahsize that it is a drawing of a seal; in this case, it is a simple round shape.
So I submit that the figure is ambiguous, and could be taken as either a character or a quasi-geometrical figure.
How do we decide? In the margins, where that clerk or later clerks have entered key words to locate or identify the text, the name is given as Dennis Conry or Conree, never as O'Conry or O'Conree.
So I submit that the clerks who copied and interpreted the text believed the ambiguous shape not to be a part of his name, and that it is better interpreted as a representation of a seal.
Either way, it is clear that Dennis, unlike many of his descendants, could read and write. His estate inventory refers to a couple of parcels of old books, unfortunately without titles, and he is recorded as having signed, not simply making his mark.