IEQp1 multiple zone system

Hello, I am working on a School project and I am currently filling in the information in 62MZ calculator for multiple zones. I have a question. Imagine a building on 3 levels which I will call LVL00, LVL01 and LVL02. Now imagine a 50 m long and 6m wide corridor on LVL01. There is also a staircase adjacent to the corridor. Through the staircases one can reach LVL00 and LVL 02. There is nothing separating the staircase from the corridor; however the staircase is separated from the other parts of LVL 00 and LVL 02. The corridor has mechanical ventilation. The staircase itself has no mechanical or natural ventilation to itself. Do you think it will be OK if I merge the area of the corridor and the areas of all the levels of the staircase and use this sum area in the calculation. What concerns me is that the corridor and the 3 levels of the staircase have different Room Tags in the drawings. Thank you in advance