First, it is important to remember that fire poles and bat poles are by and large directional—they are less than ideal for getting back up to the main living levels, especially considering the lowest floor is going to house the bar!
On a more serious note, it seems most likely to me that all of these identical townhouses were initially three story, single family homes and yours was modified long ago (and apparently done well as it appears to be “normal” in its current condition). It is also possible these units were offered as either the three story—single family unit, or the two story single family with a rental unit below. There is another possibility I will address below, and it might come into play with regard to building codes for the lower staircase.
There are (and I believe there always has been) different criteria for different kinds of stairs. Main stairs by and large have lower risers and longer treads, while utility stairs can have pretty high risers and shorter treads. They both add up to the average human stride if you add a combination of risers and treads, but utility stairs are steeper and harder to climb or descend. (Older homes which have a fancy staircase in the living room or foyer would fall under “main staircase” codes; back stairs that go from the second floor directly into the kitchen, and basement or attic staircases are usually classified as “utility” stairs and they are allowed to be steeper requiring a shorter run.) If the townhouses in your area originally called the lowest floor a “servants quarters”, they could legally have a steeper staircase with one or two, possibly even three fewer steps (if the height between floors is enough). That makes a certain amount of sense if the place always had a small kitchen downstairs (for the live-in maid to use after her shift ended). Is the front door for the lower unit subterranean? Does it seem to be retrofit into a remodel? Or does it seem to be part of an overall original design for the unit? I suppose it could have been a private entrance for the hypothetical maid anyway. Does the unit have a back door that opens to a yard or garden or alleyway? Perhaps the first floor front door was an access to egress incase the main front door was blocked by fire.
In either case, I believe your unit at one time had that lower staircase, and it was removed to make the first floor a separate apartment. If that is the case, it is even possible the property is still described as a three story single family unit. Out here in the west it is very common for remodels and additions to not be recorded on deeds or legal descriptions. If that turns out to be true, it will be very easy to retrofit a staircase back into the home. (You may need to alter the original run to add a step, or designate the lower floor as servant quarters to avoid having to add that step no matter how you actually intend to use it. If there was originally a staircase, it might also have been built to “main staircase” codes and this would be most ideal for your plans.) I hope this is all understandable; please feel free to ask questions if I have been unclear or there is more you want to know.
Also I am curious, is the electrical panel for the apartment a sub-panel supplied from your panel? Or does it have its own separate power supply and a meter? Do the two panels seem to be from the same era? Or is one an ancient fuse box with knob and tube wires running from it while the other is a modern breaker box, for example? They could both have been replaced at the same time in the past and match which tells you little, but if they are different that suggests the apartment itself was a remodel. You have some good suggestions here; I could easily have quoted at least half of the posts above to say: ‘good point’.
One last warning, there is a tried and true formula for figuring the cost of a remodel; take the highest bid and add about ten percent to it for unanticipated costs. Then double that and multiply by something in the range of 1.5 to 2.5 depending upon how lucky you believe yourself to be – and how much of a stickler you are for getting the best end product. Then just accept the fact that it will take twice as long as promised, something you love will be damaged or destroyed during the process, and it won’t end up just as you are picturing it. A week or two after it is completed, it will seem just great and well worth the money, and you will wonder how you ever lived with it before the change. There is also the exception which proves the rule; on rare occasions a remodel will come in on time and under budget; no reason your project can’t be one of these. (My last comment, and it is meant to be helpful; the lowest bid is NEVER the most affordable way to do the job, that guy left something out and he is going to gouge you later. Keep getting bids until you get several in the same range, and then pick the guy you want to spend the most amount of time with – cause you are going to spend some time together.)
Good luck !