I also just wanted to add that in the four different preschools my kids attended over the years, learning to write their first name only was a skill learned throughout the entire first year of preschool. Learning to write their last name was done during the second half of the second year of preschool. And kindergarten always spent a great deal of time working to teach kids to write their first and last names during the first several months of school. So, your DS doesn't sound far off, eventhough it is frustrating to him. But again, I know this is a tangent since you were primarily asking about how to document his abilities without his fine motor skills skewing his results.
