They shouldn't be merged. Someone listed the ESSAI under the normal circulating coin. The ESSAI with the 1750 mintage should be moved to a new entry with a number of E#6.
From world coin catalog: 1972(a) 1,750 50 Francs. Copper-Nickel. KM6. Page 2216.
The pattern, essai, piedfort, and special sets are at the end of the country listing and people don't always look there.
