In another forum I read about the "brass tacks" probably not originating from rhyming slang. Certainly they make sense in themselves.

A small percentage of slang tends to diffuse eventually into regular language, together with mondegreens, folk etymology, bad translations etc. Other parts that are no longer "cool" are still conserved as folklore.

I doubt that any true cockney would nowadays be successful when trying to introduce a new item of rhyming slang. More sarcastic jokes are now required to earn a laugh in the pubs. Besides, the cockney wearing his "titfer" earns his old-age pension as a stage figure in "My Fair Lady".