Interesting. Beautiful marbles.
Fwiw, for some reason I wrote Hero down as a Master name back in 2008.
Of course I knew it to be an Akro name but I still listed it as a Master name also for some reason. I'll try to reconstruct why I did that.
American Machine-Made Marbles says that Master acquired unsold Akro marbles in 1951. I wouldn't have guessed those corks to still be in the Akro stock then, but could be.