> I too am confused about what both authors think the definition of "ur-" is in both of their contexts.

I'm confused why you're confused. The original author (of "The seven programming ur-languages") stated what they meant by an ur-language:

> I am aware of seven ur-languages in software today. I’ll name them for a type specimen, the way a species in paleontology is named for a particular fossil that defines it and then other fossils are compared to the type specimen to determine their identity. [emphasis in original]

They didn't hide their meaning, they laid it out right before listing the languages and then explaining why they selected them.