On 7/4/99, Columbia Heights and Georgia Avenue stations were not yet open
Ah, now it makes sense!
The purpose of this "revolutionary" pattern on July 4th is to make travel more efficient for getting people to the festivities downtown and home. It was decided the regular daily routings were not nearly as good as these are.
So basically these re-routes are:
1) giving the western end of the orange line more trains
2) flipping the blue and yellow lines in VA
(1) seems fair enough for a temporary holiday fix. If (2) however is the case, why don't the Blue and Yellow Lines flip permanently in VA?