The liver sauce ("Jespi", 1.34 in MS KANTL Gent 15) was an unmitigated failure. No one, including myself, liked it. Not astonishing -- I've only once made liver sauce that I thought was really good (it was anise-based, and to this day I don't know which cookbook it was from), but this one needs lots of work before it is palatable.
For the record, the recipe was: Take 8 chicken livers and fry them until fully cooked. Blend in Cuisinart, gradually adding 1/2 Tbl. powdered grains of paradise, 1/2 tsp. ground ginger, 10 strands saffron, 1/8 tsp. clove and 2 raw egg yolks. Then blend in 1/4 cup of wine. Put in a small pot, and boil slowly to thicken, stirring frequently to prevent burning. The result was thick as paste, and the flavor was horrid: over-spiced and flat at the same time.
Future attempts should probably use a good deal more wine, to thin the sauce to a reasonable consistency. It is probably worth doing some research into chopped liver, to see if I missed any common tricks. Use far less grains, and mess with the other flavors to try to make the flavor less flat.
The mustard sauce (1.32 in the same source) was a qualified success -- not bad, but needs work. The recipe is quite simple. Grind 2 Tbl. mustard seed with 1 tsp. grains of paradise in a spice mill until mostly powdered. Mix into 1 cup of unsweetened applesauce.
While this was okay, it lost a lot of potency overnight: it didn't have nearly as much kick at the feast as it did right after I made it. So this one may need to be made day-of. Also, the flavor is again a bit flat -- note that it involves no vinegar, a staple in many mustards. Might try kicking up the grains, and see if that helps.
The galengale sauce ("Galentijn", 1.24 in the same source) was the one real success. Mildly sweet and reasonably spiced, this sauce is essentially a thickened hypocras, and probably works in places where you would expect a sweet sauce to work. I thought it went decently well with the poached salmon. The reconstruction, including notes, can be found in our cookbook.