Has Krause Got It Seriously Wrong?

The French predecimal monetary system is confusing, but the heart of the problem is that the exchange rate between sous and ecus was not fixed; it changed. All coins in circulation were given a face value in livres, the money-of-account. When originally introduced in 1641, the silver ecu was worth 3 livres (60 sols). Inflation caused constant official revaluing from 1690 until it finally stabilized at six livres (120 sols) in 1726.

So, as I understand it, a 1/12 ecu coin was worth either 5 sols or 10 sols, or some value in between, depending on when exactly you're talking about. Under the circumstances, it's probably best not to assign fractional-ecu coins a value in sols at all.

I suspect the reason for Krause's attitude is that Krause has worked backwards in time; they wrote the 1700s book before writing the 1600s book, basing their work on the Craig catalogue which only went back to 1750. In the mid-1700s, the coin was 10 sols, so that's what the coin was put down as in the Krause database. The French and German catalogues, on the other hand, presumably take a more holistic point of view and consider what the coin was originally issued as, in the 1600s.