too easy! Cardenio is a giveaway.

A very good grid with lots of fair ingenuity, and I got most of it. I understand the cleverness behind 'Cardenio', and I got that group by elimination, but it's not really a fair solution given that the attribution is not uncertain (and I have Literature degree) and we know more or less nothing about it.

Never heard of Cardenio, hence I struggled on the Shakespeare link. It shouldn't really be in the grid, given the doubt that it's actually one of his plays.