OK, I've done some digging and have found references for part of my claim. As I've claimed all along, you got to know more than the printed rule, you've got to know the intent of the rule and a little history to understand some of the compactly written rules...
Look at the wording and interpretations
before the change from the
04-05 rules interpretation sheet (highlighting mine):
Situation #8:
As the official calls a traveling violation, he/she properly sounds the whistle and gives the signal to stop the clock. While doing this, the official is able to see the exact time remaining in the fourth quarter. The clock shows 55 seconds remaining. The timer stops the clock: (a) at 55 seconds; (b) at 54 seconds; (c) at 53 seconds; or (d) 50 seconds.
Ruling: In (a) and (b), there has been no obvious timing mistake. The timer should be able to react and stop the clock in one second when the whistle is heard and/or the signal is seen. However, in (c) and (d), more than one second of time elapsed from the time the signal was given until the clock was stopped. The referee will order 55 seconds put on the clock in (c) and (d). (5–10–1)
Comment: By interpretation, “lag or reaction” time is limited to one second when the official’s signal is heard and/or seen clearly. The rules do not permit the referee to correct situations resulting in normal reaction time of the timer which results in a “lag” in stopping the clock. Additional time which may subsequently run off the clock (after the one second lag time) is considered a timing mistake and may be corrected.
Now, look at the wording and descriptions after the change...Comments on the 2006-07 Basketball Rules Revisions
LAG TIME ELIMINATED (5-10-1): This change eliminates the need for lag time or reaction time on the part of the clock operator. The referee may put the exact time observed by an official back on the game clock. The committee felt that with new clock technology and the ability to observe tenths of a second, when an official has definite knowledge relative to the time involved, he/she should have the ability to put the correct time on the game clock.
So, the NFHS, in 04-05 considered 1 second to be the threshold between mistake and non-mistake....as it was beyond the allowed lag time of 1 second. Now, they've "ELIMINATED" the lag time, not cut in in half, not cut it by 4....but eliminated. The comment CLEARLY says the clock operator's reaction time is eliminated and when the official observes a time on the clock, they may put it back and should have the ability to put it back.
Now, onto the 2nd point....whether it is "optional" or not. Note that the comment says "may" and has the "ability" to put it back but doesn't use the word "shall". That is a little less clear but that grants the official the option of not restoring fractional time when there are 5 minutes left or when it is a 20 point differential with 4 seconds left. I know there is some other source that talks more directly about this but I've not yet located it.