Here's the thing, though: the back of the PHB has an oddball section called "The Adventure" which serves to introduce and organize standard D&D adventuring activities for the new player. In the historical sequence, obviously, the was written after OD&D was complete but before the DMG. It hints at rules in non-mechanical terms (you might say "flavor text") that will be presented in full detail only for the DM later in the DMG. As such, it includes the germs for numerous ideas for changes and alterations from OD&D, that were then dropped or reconsidered when the DMG was actually completed.
It's easy to overlook these ideas due to their placement, disagreement with the later DMG, and the fact that they are not generally included in the combined index at the back of the DMG. (For example: No "parry" rule is listed in that index). But here's what I ran into today, accidentally looking at the subsection on "Melee Combat":
Participants in a melee can opt to attack, parry, fall back, or flee. Attack can be by weapon, bare hands, or grappling. Parrying disallows any return attack that round, but the strength "to hit" bonus is then subtracted from the opponent's "to hit" dice roll(s), so the character is less likely to be hit. Falling back is a retrograde move facing the opponent(s) and can be used in conjunction with a parry, and opponent creatures are able to follow if not otherwise engaged. Fleeing means as rapid a withdrawal from combat as possible; while it exposes the character to rear attack at the time, subsequent attacks can only be made if the opponent is able to follow the fleeing character at equal or greater speed. [PHB, p. 104-5]So: A rule for parrying somewhat hidden in the PHB, not reiterated in the DMG, and not included in any index. A rule that's different from the Chainmail (OD&D) rule, in that the -2 modifier is replaced by the user's Strength "to hit" bonus -- and hence only usable by those with exceptional strength, and of very small benefit even to them (in AD&D, +1 from 17 to 18/50, +2 from 18/51-99, and +3 from 18/00).
Have you ever used that PHB rule?