Sterling = super pastel/cinnamon....the snake is a super pastel and a cinnamon.....it is expressing those traits at the same time.
Silver streak = super pastel/black pastel
Pewter = pastel/cinnamon OR pastel/black pastel
A sterling and a silver streak are very similar......you just use different forms of the same mutation to make it. Both sterlings and silver streaks are a "step up" from cinny pewters and black pewters.
Some of the confusion surrounding these morphs comes from different names for similar looking morphs (some breeders feel it is justified while others don't).
But a lot of the confusion started with the snake with original sterling moniker......it was most likely misidentified. The breeder called the snake a sterling when in reality it was probably an exceptional super pastel (not a super pastel/cinny). It didn't look like the sterlings that were produced after it. Not sure if subsequent breedings proved if it was a super pastel or not......it should be around that size/time right about now. Not only were the pictures posted on forums but they were posted in a couple of the nicer bp books too.
Here is an old picture of my sterling:
If I get around to it, I'll post some updated pics.