Generally this was found in older buildings from the 1800’s - early 1900’s. It could be any of the options you list. In some cases the stairs could have been the only access to the upper level.
Often a building like this would have a business like a small store on the main floor, with living quarters for the storekeeper and his family in the upper level. There would probably be an internal staircase to connect the shop and the living area, but the external one allowed the store owner’s family to access their ‘home’ without having to go thru the store.
If the owner didn’t live there, the upper level could also be made into one or two rental apartments.
In the 20th century many cities passed ordinances requiring living areas to have two means of entrance/exit (in case of fire) so again there could be both an external and internal set of stairs because of that.
In the photo, the “store” area appears to have a double door between the two large display windows. There’s another door on the front wall, at the near corner, which would usually lead only to a set of interior stairs leading to the second floor. I would have built that kit with the exterior stairway wall on the opposite side of the building - that way, the bottom of the stairs could have been connected to the street with a short walkway, and the upstairs could have represented two separate apartments. Either way, though, a nice-looking structure.
I have to agree with Doctorwayne, there appears to be an interior staircase on the left side of the building. The 2nd floor window at the back would be on the landing of that staircase. Could be there are two apartments/offices on the 2nd floor, a front and back (although typically apartments are oriented so there is a left and right one.) Either way the stair is plausible.
Thank you for the quick answer. I understood the outside stairs are optional. I can make a story to have them inplace but can omit them also with another good story. That’s great as i gives me the freedom to arrange them as I need it.
Between 1966-1971 I lived in Corpus Christi, Texas in one of four apartments above a group of stores. There was one interior stairway just inside an entrance in between the storefronts right in the middle of the building. At one time, the landlord had an office where I could pay the rent there. There was also a wooden outdoor stairway at one end of the upstairs hall. I could come or go either way. In recent years, I have seen the outdoor stairway collapsed.
I have seen a few buildings were the stairs were on the outside coming down to the front. They lead to a common hallway or landing across the back for two or more offices or apartments upstairs. Some even had the stair case walled in and a roof for weather reasons with or without a door at the bottom.