Just a thought,
could -33 be referring to the centre disk itself, perhaps in relation to brake caliper clearance or something like that? (not sure why they would use - though)
For example Work use disk codes of (A Disk- Standard) (O Disk- Deep rim) (T Disk- Big caliper) Maybe R Disk too?
Having seen these in real life I did notice that the centre disk was angled back a fair bit, but I was skeptical that the offset was -33, Negative something yes, but not -33. Therefore I think it could be Referring to the centre disk itself.
Perhaps these are a special order model, for use with bigger calipers.
Any thoughts?