I found a copy of the ASA rules for 1989 as reprinted in a the National Association for Girls & Women in Sport and it includes the DP rule. You can
download the NAGWS manual here.
The DP rule was pretty much the same then as it is now, so we have had this rule for 20 years (at least) and people still don't understand it.
Does anybody know what year this rule was first in place?