God rest Schadenfreude, a brilliant puzzle with no ambiguities and no tedious grid staring. The southwest corner had me stumped for far too long, due to difficult, but fantastic clues.
Eight of the works are listed with the same numbers on at least two sites. I'm still trying to confirm the numbers intended by the setter for the other three. Wikipedia is notoriously unreliable, so I wouldn't want to rely on that.
The key phrase in the preamble is “The clashing letters specify WHOLE thematic items EXACTLY . . .” The three items that require the secondary system were also the sources of other items that typically incorporate the thematic items given by the clashing items as part of their names.