Flowmaster Muffler Models Quick ?

Quick question...does anyone know if you can tell what model Flowmaster a muffler is from looking at it? I got one put on and am not sure if it's the original 40 series or the delta flow.

I have the Flowmaster Original 40 and I can't tell what it is. Why, you don't trust the guys that did the job or what's up?

Well I just remember asking for the original 40 but I seem to remember the receipt had the serial # for the delta flow. I thought it was possible they installed the original 40 series but for one reason or another just listed the delta flow on the receipt.

Anyone...?