From your example and from formulas on sheet DIREPs, it looks like DIREP is additional characteristic of document - parallel with DocClass. When this is the case, then you don't need additional sheet, but you need additional columns for DIREP indo in documents table.

At same time, from you having DIREP types listed in dropdown of DocClass, this assumes DIREP type are another document classes like release, training, etc. When this is the case, then a document can have only one of them selected - this means you need additional helper columns after column DCM in documents table. And again - no need for separate DIREP table.