Well, somebody's got it wrong, and of course it's hard to say who.
This is why I originally asked the question, because I wasn't sure. I don't see how a dog as famous as Gr Ch Buck (or dogmen as good and famous as Barney Fife and STP) could have "got it wrong" as to who Grand Champion Buck whipped for #5. Keep in mind, STP also owned Yellow's sister, so he
has to have some idea about who Yellow and his littermates are. This is the direct quote from Barney Fife:
"In Buck's 5th he went into Rodney's two time winner JR, littermate to Gr. Ch. Yellow ROM. JR was handled at :52 minutes and could not go any further. JR later went on to win three more."
I mean, how many "JRs" can there be, that were brothers to Yellow, and who also won a total of 5x?
It seems either the top veterans STP and Barney Fife are wrong ... or some "old man" is wrong (or, possibly, the old man and those associated with JR are trying to sweep a disappointing loss under the carpet

).
Anyway, it's hard to say for sure, since none of us was there, but it is an interesting factoid nonetheless.
Jack