IWC 5057272 - Strange Model/Serial Number

I have a Portugese Perpetual model / serial number 5057272 - I can't find this model number listed anywhere - could anyone please help.

It's the individual case number of your watch.

Hello Abullen

As Tilo said, the number engraved on the case back of your watch is the individual case number (what you may call serial number). This number is unique and used to identify that one particular watch.
The model number (IWC calls this the article or reference number) is not engraved anywhere on your watch, but can be found on the international warranty card that was issued with the watch.