My suggestion would be for you to consider using a Z clause to give definition to Overseeing Organisation eg 11.2 (??) for Appendixes ??, ???, ???? the Overseeing Organisation is the Employer, for Appendixes XX, XXX, XXXX the Overseeing Organisation is the Project Manager etc.
Regarding the difference between information to be included in the Works Information and that to be in the Site Information you could prepare a schedule of which Appendices were in which section and refer to that schedule in the Contract Data Part 1 (the Works Information is in ................ The Site Information is in .....................). Care would be needed to ensure you got the right information in the right section; remember the importance of the Works Information.
Regarding the difference between information to be included in the Works Information and that to be in the Site Information you could prepare a schedule of which Appendices were in which section and refer to that schedule in the Contract Data Part 1 (the Works Information is in ................ The Site Information is in .....................). Care would be needed to ensure you got the right information in the right section; remember the importance of the Works Information.