[re-articulation of a previously asked question]

BACKGROUND
I'm calculating workdays to determine a days count between the LAST
updated
date and the completed date; this is to measure our scheduling
accuracy. Can
you assist?
Current formula is: =IF(OR(R7=""),"",NETWORKDAYS(L7,R7))-1
a) the original date is L7
b) the completed date is R7
c) M7 through Q7 are updated delivery dates (date changes)

REQUEST
New formula result required: the difference between the LAST date
updated
and the completion date.
1) if the schedule doesn't change, the difference would be between L7
and
R7. It is possible that the date could have changed up to 5 times (M7 -
Q7), so the calculation would use the last date change rather than L7.
2) Also, I don't want this count to appear until there is a completion
date
in R7.