Assuming i have the MASTER and other variuos sheet into same dir
(c:\mydir\)

Into MASTER and into other sheets is present a column L with unique
index value. (not possible dupes).

http://www4.rapidupload.com/d.php?file=dl&filepath=4193

Is possible via macro:
From a macro into the MASTER wbook, auto insert in the column M the
variuos value present in each from all column M of other sheets
4506...., 4507.... and 4508...? Make this operation without to open the
variuois sheet 4506...., 4507.... and 4508...from the mydir...
Note: in the offcial dir are present many wbooks named 4500...,
4506...,4501...,4502.....