[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).
2) Also, I don't want this count to appear until there is a completion date
in R7.