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

[degaskell]

I re-read my sources on ducats, gulden, and thaler, and I'm still not sure I'm understanding them correctly, but I think this is the main relevant history (if not, I invoke Cunningham's Law):

• The original "florin" was a 3.5g gold coin from Florence. Various other nations (starting with Venice) minted equivalent 3.5g gold coins that became common trade coins in the 13th-19th centuries, going by the name "ducat".
  
• The "Rheingulden" was initially a German version of this coin ("Gulden" deriving the word "gold"), but was debased over the next few centuries until it was worth less than the common trade ducat.
  
• The "Rheingulden" was eventually adopted as the "Reichsgulden", a standard national gold coin for the Holy Roman Empire. Confusingly, this was also called a "florin." A flurry of complicated value changes followed as the HRE tried to get everyone on the same standard.
  
• In the mid-1500s the HRE tried to turn the Reichsgulden into two equivalent coins, the gold "Gulden" and the silver "Guldiner" (Guldengroschen). But, economics being what it is, it was hard to keep the values equal, so after a few decades of confusion the HRE introduced the silver "Thaler" as the standard trade coin. After this the "Gulden"/"Florin"/"Reichsgulden"/"Rheinische Gulden"/"Goldgulden"/whatever stopped being widely circulated as an actual coin, but was retained as a notional currency unit for recording transactions (a bit like keeping your records in dollars even if you only ever actually pay for things in quarter coins). One Gulden was worth slightly less than one Thaler.
  
• The HRE also minted "Ducats" during this time, which were Florentine-style 3.5g gold coins (in theory worth correspondingly more than the notionally 2.5g gold Gulden by weight, except that I'm not sure the Gulden was actually still equivalent to 2.5g of gold at this point since its value was now defined relative to the value of a silver Thaler).
  

Over the next few centuries the conversion rates changed even further (I saw one source quoting 1 ducat = 4 thaler), and in 1690 the whole system switched to a "northern German Thaler" and a "southern German Gulden", both of which were now based on the value of the circulating silver Thaler coin, but neither of which was equivalent to their former definitions, nor to the actual worth of 1 silver Thaler coin.

So, it seems to me that the Karl Widemann transaction was most likely actually paid in silver Thaler, but was conceptualized as a transaction of 600 gold Gulden (florins) because that was the standard accounting unit at the time. For Marci to interpose "ducats" is not actually that much of a stretch, since that was the main gold coin of his day and similar coins were elsewhere circulating under the name "florin". Of course, another complication is that Marci's letter is actually in Latin and uses the phrase "600 ducatos," which should presumably be translated "ducats" but is colloquial Latin at best. So, I think Rene is probably correct in not overinterpreting what Marci meant beyond "600 gold coins."