"This tells me that the exact year of engine manufacture is suspect. The engine could have had a dented valve cover and a previous owner swapped it out."

Maybe so, but the newer version valve cover would need four attachment screw holes drilled into an older head?

"The engine serial number, block & head casting dates and numbers are better identifiers if you are seriously wanting to determine the year(s)."

Yes - good advice - here are locations of various codes on 1954 and later 235 engines (and on all 261) engines. (on all USA engines - Canada & Australia might be different?)