What Jr4, Classic 7, etc. mean in terms of layout

Classic 6 is a 2BR, 2 BA with a Living room, full dining room, kitchen, powder room and a maids rooms +bath. Classic seven is the same as above plus another bedrooms and bath.

Classic 5 has one less BR and Bath.

JR four is a straight 1BR, bath, LR DR and kitchen.

1BR has no DR.

Classic 6 - 2 bedrooms, living room, dining room, maid's room, kitchen. Usually 2 main baths, and a maid's half-bath (though the latter is missing in some small 6s)
Classic 7 - 6 + 1 bedroom. I have seen 7s with 2 bedrooms and 2 maid's rooms.
Classic 8 - 6 + 1 bedroom, 2 maid's rooms. Rarely is it a 4-bedroom, 1 maid's room setup.
Once you get at or above the 7-room count, there are apts with a reception room - what that means is usually one less bedroom or maid's room.

Classic 5 - Classic 6 minus maid's room. I have seen some 5s with 1 bedroom and 1 maid's room.

So is the maid's room what makes something a "classic" anything? In other words a regular three bedroom with a living room and dining room wouldn't be referred to as a classic 6?

On a related note, do most people that live in apartments with a maid's room actually have maids or nannies or something? If not, what is that room good for?

Sorry for naive questions, I've lived in NYC for 10 years but most of this stuff is alien to me.

"Classic" refers to an upper-middle-class apartment with certain gracious details (i.e. set up for entertaining) in a large-ish elevator building that usually dates from 1900-WW II.

The maid's room tended to drop off in the 1920's, when immigration laws made servants harder to come by . . . although those usually have a WC and even a dressing room for the day-help, off of the kitchen. Still, I think a Classic 5 is a dodgy proposition, and RE Brokers will soon start telling us about Classic Ones and Alcove Classic Ones.

Most people don't have maids/nannies living in the maid's room, or at least not for long -- they quit at the drop of a hat, and don't like living in anyway. Some maid's rooms are configured hopelessly, but some are reasonable large and useful. At least among anybody I know, one of the children winds up in the maid's room. Or it's obliterated by combining it with the kitchen.

some people use the maid's room as a den or office