Building plans don't call out every little detail
The differences in layout between the buildings are expected. You may be largely correct: the installations likely were done by different crews and without precise layout diagrams. That's normal. Plans for a building specify a variety of things like which plumbing fixtures, light fixtures, or fire detectors and horns/strobes need to be installed and approximately where they must be located. Most of the time the locations are quite flexible. Plans would not dictate exact placement of the pipes or electrical wiring. It's not practical. Likewise they would not dictate the precise arrangement of the furnace etc in a unit, nor would they dictate the exact placement of the various fire control panels in the riser room.
Fire alarms can work fine with either style of switch
Fire alarm systems deal with alarm events, tamper events, and supervisory events (sometimes there's no distinction between the latter two). Events cause notifications; virtually all events cause a signal to be transmitted to the monitoring service. A fire alarm panel will typically have multiple inputs. Some inputs go to detection devices and trigger an alarm; other inputs go to tamper or supervisory sources and only trigger a report to the monitoring service. Often an input can be configured for either normally open or normally closed operation. Whether NO or NC is chosen by the designer or installer depends on a variety of factors, but most often the detection job can be accomplished with either. Your RTS is offered in both NO and NC styles to accommodate this flexibility. Building plans often will not require a specific style of switch.
Why would a fire alarm system include a room temp switch, anyway?
A room temperature switch is not likely to control anything; its purpose is purely to monitor ambient temperature in a riser room, attic, etc -- places where a freeze could impair the automatic sprinkler system and could go unnoticed because the space isn't occupied. If the switch trips a signal would be sent to the monitoring service, who should then forward the information to the appropriate building management representative who should then investigate and correct the situation.
Inspection verifies it all works
The system should have been inspected and tested for correct operation when it was commissioned. Periodic re-testing may be required by law depending on where you are. It might also be required by a fire insurance carrier. Of course, testing may also be commissioned at any time by a proactive building owner who just wants to be sure that life safety systems like this one are dependable.
Practical difference in zone wiring for NO versus NC
It's true that NC and NO switches won't work exactly the same - the circuit as a whole has to be arranged differently. Suppose I'm a fire alarm installer (and I was, for about a year) and my work order calls for a room temperature switch on a supervisory zone of its own.
If I want to use an NO switch then I might use two-conductor cable to connect a zone input and common to the two terminals of the NO switch. I'd connect the end-of-line resistor across the switch terminals too. Then I'd configure the panel so that if the zone opens that's a wiring fault and if the zone shorts that's a supervisory alarm indicating the room is cold.
If instead I want to use an NC switch then I'd still use two-conductor cable from zone input and common at the panel. One conductor would connect to a switch terminal, the other conductor would connect to the EOL resistor, and the resistor would connect to the other switch terminal. I'd configure the panel so that if the zone opens that's a supervisory alarm indicating the room is cold.
The latter approach doesn't provide any electronic method of distinguishing between a wiring fault and a cold room condition. Maybe that's a little inferior, but if the job specs didn't require differentiating the two, then according to the job requirements the two approaches are equally valid.
As an installer I'd do either one based on which kind of switches I have on hand. Maybe I prefer to use the NO switch but somebody ordered some NC by mistake, or they were left over from another job, or the supplier was out of stock of NO so we bought NC instead..
It's impossible to guess why the systems were built with different style of switches, but yes it's wrong to expect that two similar ("identical" to untrained eyes) buildings built years apart would have their fire systems set up exactly the same way.