Good question, it would be hidden. You'd ask a guy wtf "Lady Godiva" meant and he'd say "Fivah". The animals for numbers, I don't remember. Possibly some connection ages ago that you similarly needed to have the story for.

Ah, I incorrectly inferred that you were involved in the creation of the slang.

It is London slang, but it isn't necessarily Rhyming slang. In fact, these terms are generally understood to have originated as racing/bookmakers' slang, and go back to at least the end of the 18th century. This is a 19th century slang dictionary.

* https://archive.org/details/slangdictionarye00hottuoft/page/...

At first I was skeptical and assumed that you had not realized the parent comment to which I had replied. But I checked and was still skeptical when I checked 'monkey' but indeed there was an alternate definition that was numerical. However I can't find one for 'donkey'. But maybe the parent's memory is faulty or more recent slang has added these numerical denotations in a greater context than just the parent's past workplace.

One of those lemmata casts doubt on the veracity of "Port Out, Starboard Home." I also enjoyed the dual meanings of pot-walloper, similar to "cutting coupons" shifting semantics at opposite ends of the NRS social grades.