Should the "600 ducats" part of the Rudolf story be dismissed for good?

[pedestrian]

a couple in English is understood as two or three or four..

In English a couple means two. However it is often used loosely to include three or four. Anything more than four I would have thought stretches the word beyond its limits.

You've never been out for a couple of quick drinks after work?

Also perhaps never been to the South Atlantic islands - St Helena and Tristan da Cunha - where the English in use today sounds curious and at times barely comprehensible to other English speakers but is thought to be similar to 18th century English dialects, presumably those from southwestern England. I believe the theory is that the population - especially for Tristan, <300 people - is too small for linguistic drift to have occurred.

In St Helena 'a couple' means several, while 'a nice couple' means 'quite a lot'.