I believe the 1997-2000 rule book is when Appendix E first appeared of which I have a copy.  I also have a copy of the 1993-1996 International Yacht Racing Rules that has no mention of Radio Control Sailing.

Radio sailing history (onemetre.net)

This is an online history

Thank you Richard but this does not answer the question.
It seems that there was an appendix in the 1993 rules, but many editors did not publish them.
I would like this to be confirmed.

In my copy of Elvstrom 1989-92,  Appendices 1 to 14 are listed, none of which refers to Radio or Radio Controlled sailing.

In my copy of Perry, Understanding the Yacht Racing Rules through 1996 There is a reference to Appendix B7 Racing Rules for Radio-Controlled Yachts

Then Appendix E appeared in the 1995 rewrite.