I always understood that "taters" came from Cockney rhyming slang

That's a new one on me. The phrase "taters in the mould" sounds a bit long for Cockney slang, which is usually one or two words, excluding connecting word (which is usually unstressed): "Boat Race", "Plates'a (of) Meat", "Trouble'n (and) Strife". It doesn't seem to have the right rhythm, either. Still, you could be right - I'm no expert on these matters.