Depends on th3 y3ar of th3 car - W109s and early 129s were badged/branded as 500SLs but later during mid life the 129s were badged as SL500s... (mid nineties...)
Well that's clear then, so basically what you guys are saying is that the guy at MB, paid to make up the names, was, how can I put it, inventive, creative, or maybe just sleeping