9 or 10, there is a difference

Here is the Clay connection which probably by-passes the problem with John Ellison Austin.  This will tell us about the markers for Arch Sr., if I can get him to donate his Y-DNA.  Got any persuasive words?

Clay⁷ Austin (Joseph C. Jr.⁶, Joseph C Sr.⁵, William⁴, Archibald Jr.³, Arch Sr.² Austin, Edward Riggs¹).  Clay may be either a 9 or 10 at marker 47. I’m convinced that if Clay is a 9, then Arch Sr. is a 9; and if a 10, then Arch Sr. is a 10.  Is this right?

This will tell us 9 or 10 at marker 47 for Arch Sr.  Help me out here, please.  This seems easy; but it’s not easy to me.

If Arch Sr. is a 9, as you expect, then will that indicate/prove that the mutation to 9 occurred in Arch Sr. prior to his having sons Clisbe Sr. and Arch Jr.? Or will it prove he is not a son of Edward, who is surely a 10? Or, is it really that we can’t differentiate between these two distinctly different possibilities? Are the probabilities of the two quite different?

If Arch Sr. is a 10, then what would be proven? Will that prove that the mutation to 9 occurred in Clisbe Sr. prior to his having children?... cause we know Clisbe Sr. is a 9.

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Alvy answer:
 

If Clay7 (using your nomenclature) has a 9 at marker 47, then almost certainly Arch2 Sr. does too.

If Clay7 has a 10 there then we just don’t know whether Arch2 Sr. has a 9 or a 10 and would have to say it that way. In that case, it would be POSSIBLE (but not proved) that the 10 came from Edward5 and was (I’m just hypothesizing here) the same 10 passed down to Horace and Roy. That’s consistent story, but unfortunately unproved. It just doesn’t DISPROVE it, which is good.

There is no reason for two sons to have exactly the same YDNA as the father. A mutation has to happen somewhere, typically in a procreative event.