Need help determining Age of HVAC All-In-One Units

Specific Inspection Topics Inspecting HVAC Systems
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I need to know where to find or told how to determine the age of the following All-In-One HVAC Rooftop Units. Any help would be appreciated.

Thanks

  1. York - Model#: 03CG090N13025E ; S/N: NDCM032780
  2. York - Model#: 02CG120N200258 ; S/N: Unknown could not read MFG tag
  3. York - Model#: 03CG090N16525C ; S/N: NEBM031888
  4. Comfort Maker - Model#: PG8090H2HA; S/N: L970574154
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hope this helps

Anatol