Well, Terry, I started out racing go karts at 12 years old. Had a favorite uncle who was a well known sports car racer & was bitten by the bug. By '62 I was ready for my first real race car, a '47 Crosley Hotshot tube-chassis special. With the cam, triple carbs & a Darrin glass body [and lots more!] it wound to 12 grand & set a course record at Cotati back then, turning 97 mph laps.
From there I turned to foreign sports cars because American mfgr's still hadn't figured out that actual handling & brakes would be nice, in addition to their lumbering, low rpm V8's. There was no working concept of power to weight ratio in Detroit either. All they knew was chrome to V8 ratio. So, I knew Daimler Benz & Mercedes well back in those days & so did many others. Most go fasters back then called Daimler Benz cars 'Benz' for short.
Just like Maserati's were Maser's & Ferrari were Fazazz, so Mercedes were also called Mercs. The first Mercedes cars, named after Karl Benz's daughter, were sold in 1926 & were soon called Merc's: the name stuck.
The first American Mercury came along in 1939, 13 years later. So it looks like Mercedes Benz were called Mercs long before American Mercury existed to make a name for itself. When I lived in Germany the Mercedes were also referred to as Mercs by locals, a popular nickname from years before.
Didn't say we or you had to like it, just the facts of it...