Thanks, but this is still confusing. And I do not see it would deal with any issue of a shortage of flight numbers.

In the last week UA1426 has been LAX to IAH twice. That is not to say that the remaining 5 days there is no LAX service. And given that the IAH MID flight is at 8pm, there is guaranteed to be a LAX IAH flight arriving within a couple of hours of its departure (is there not?) So why not say that UA1426 is ALWAYS LAX IAH MID but the time of the LAX IAH segment changes? And then that frees up any numbers that were previously used on LAX IAH on the other 5 days when 1426 does not operate LAX IAH