Question about Protected Stairways for Basements (in Dwellinghouses)

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I'm looking at Approved Document B for Dwellinghouses.
I'm struggling to figure out if basements can use any normal protected stairway layout or if 2.16 is saying that it'd need to connect to a final exit in a specific way. Specifically whether they can use the separated routes option that is detailed in 2.5a and diagram 2.2b.

Perhaps the answer is obvious to a more experienced eye. Does anyone know?

Context is desired:
A friend looking at buying their first home. Most likely (given budget and locale) the fairly typical 2 up 2 down layout (where the basement stairs are sandwiched between the kitchen and living room with the final exits on the front and rear walls.
Ideally (given the terrifying cost of housing) they'd like to be able assess whether they could convert the basement into habitable rooms when looking at houses.
Just for convenience, the relevant sections of approved document B that I know about are: 2.16, 2.5a, diagram 2.2 and that "Protected Stairway" entry in appendix A.

(Feel free to drop other useful advice if you have it.)