BS5588 is still guidance, regardless of being withdrawn. Same as CP3. Its old, its dated, but it is perfect guidance to consider when undertaking an FRA. THe key to undertaking an FRA in old tower blocks / ressy building, is to have an idea of how these buildings were designed. Many fire fighters think they can undertake FRAs, but without knowing how these buildings were intially designed, this is where unsuitable and unsufficient reports are produced.
Now with regards to the intial query. Relating to AD B, BS5588 and the sleeping guide. They all say a similar thing. For purpose built blocks up to 4 floors above ground (G+3), you can have two flats opening onto the stair without ventilated corridors. Flats can also open onto the stair if they have internal protected hallways, however RRO FRAs are non intrusive of flats, therefore difficult to ascertain.
If you have four floors above ground and there is still no ventilation to corrids, unless the corridors are located next to external walls, it is unrealistic to acheive. You need to assess the risk. It is reasonable to assume that the increased risk of the additional floor is legligable, compared to the cost of constructing ducts or voidds to provide ventilation to the corridors. I have an FRA of a block exactly the same (I think). PM me and i'll send you it.