How objective or subjective is apartment classification (A,B,C)?

[Nick B.]

Hello BP,

Are there any specific set of features that must be present or absent in a certain apartment class?

Here are few items that I sometimes get confused about:

• Age: 0-10 - "A", 11-20 - "B", 21+ - "C" - this is a general rule for a generic apartment complex in a suburban area and does not apply to places like SF or NY where location trumps age. I get that. However, I often see 15+ y/o properties offered as "A" class. Can a once-upon-a-time "A" property still be considered "A" 15 years later comparing with "B" and renovated "C" properties?
• Amenities: I was once presented a 20+ y/o property in Ohio that had in-windows A/C units. The deal sponsor marketed it as a "B" class. Yet, here in DFW, many "C" properties have standalone A/C units. Should a "B" class property have standalone A/C units as a rule?
• Appearance: a property looks like a "C" class from the outside and based on age but some units have really good interiors and the property is deemed "B" by the sponsor.
• Expenses: does it cost less or more to run an "A" class property than a "C" class? I saw "A" being underwritten to lower expenses than a "C" class. Does it make sense?

So, is there a set of rules to classify apartments or for the most part the beauty is in the eye of the beholder?

Thanks
Nick