Bonanza is set in the 1860's, yet during the episode, Wayne Newton sings "Danny Boy". This song was written in 1910 re-tuned to "Londonderry Air" in 1913.
The songs featured are not correct for the Bonanza era.
"The Old Rugged Cross" was written in 1912.
"Danny Boy" was written in 1913,
"Scarlet Ribbons" was written in 1941.