The actress Pandora Spocks who played Serena on Bewitched was actually the same actress who played Samantha Who?

That statement is incorrect. Pandora Spocks played the character Serena on "Bewitched," but she did not play Samantha on "Samantha Who." The role of Samantha on "Bewitched" was famously portrayed by Elizabeth Montgomery, while Christina Applegate starred as Samantha in "Samantha Who."