Generally with Mercedes a higher number is a newer number.
Cynics raised in the American car culture will think that this means Mercedes found a way to source the part cheaper, but the fact of Mercedes life is usually that it's an improved part.
Parts having to do with safety are a dumb place to buy used parts and a dumb place to make dubious substitutions.
You of course can look up all the Mercedes part numbers you want by subscribing to EPC.
http://epc.startekinfo.com