Two different animals:
Over Running is a One way clutch which allows Alternator to freewheel
(Less load on serpentine Belt drive system)
Thereby SAVING:
The Harmonic Balancer
and
Spring loaded tensioning system.
Decoupler Pulley is also an One way clutch WHICH has a spring that allows
SOFT engagement of the Alternator's drive.
Gates application chart for the clutches they offer:
http://www.gates.com/oreilly/tech_tips/GATES%20ADP%20BROCHURE.PDF
Please note: Gates does not manufacture any of the clutches.
INA which is a division of Schaeffler (Along with LUK, Rueville and FAG)
provides Gates with it's clutch products.
'çannot prove ,but believe INA is OE supplier to Diamler (A.K.A. Mercedes)
Welcome to the Schaeffler Group
Schaeffler Germany | Company
If you plunder around the Gates page you'll see an application for the
'96 - '97 E300D that requires "No Special Tools"
Gates part # 37011P
But Gates does offer the "Tool Kit" (Which is applicable to all pulleys)
Keep in mind that all this overrunning/decoupler clutch action ONLY began
a few years ago.
AND that the Home Market (Deutschland) probably saw them in use before
North America.