The Player's Handbook had a TSR ship date of March, and an on sale date of April.
The Dungeon Master's Guide had a TSR ship date of May, and an on sale date of June.
Monstrous Compendium, Volume One had a TSR ship date of June, and an on sale date of July.
Monstrous Compendium, Volume Two had a TSR ship date of August, and an on sale date of September.
For some reason, the copyright registration dates are slightly different, with a date of 1989-02-10 for the PH, 1989-05-01 for the DMG, 1989-06-20 for MC1 and 1989-08-23 for MC2.