DS-6620B or 210-AZLH

Hi Dears ,

What is the difference between part number DS-6620B and 210-AZLH?  And in general, why don't Dell equipment have a specific part number?

I need a part# for this spec " DS-6620B FTR switch w/24 32G Sfp , V2   "  so that i can see the information with Part# on Dell website