One other thing to consider about the Buckner claim and old flags of the KSG:
One of the core brigades of the Army of Central Kentucky was the famous Orphan Brigade, most of whom had been in the Kentucky State Guard before the war, especially its officers.
Thus seeing a new flag that was like the one they had mustered under in 1860, was not far off base for them to rally around. The 2nd KY of this brigade also had their First National flag too at Donelson.
Please keep in mind that these claims of heritage and flag creations are late 19th/early 20th Century creations and not from the time frame when the flags were actually created.
The Buckner claim has loads of better evidence for it to be valid than the Irish claim.