Regarding the Lucite guitar, I remember asking Neil Lilien about it, and he said, it was made specifically for that ad, and didn't elaborate further.
As mentioned, very often, prototypes and one-offs were bought by dealers or sales reps when we were done with them. Lilien and Tell were all about selling anything and everything they could, knowing they had to answer to the honchos at Advent Corporation. I remember the days when they both came in wearing suits, because they had to go to Manhattan to meet with corporate.
At one point, Lilien was strongly considering making piano benches for some company at the factory in Westerly. That never came to pass.