Eric,

I think you are right about the date codes. Looks like your set and the one on eBay both have replacement RCA tubes.

The 1958 Allied Radio catalog does not list the 21CYP22 or 15GP22, but the 21AXP22 appears with a list price of $160 and net of $127.40. The metal cone type 27MP4 is only 93 cents less!