Well 10 years old could be borderline, depending on when the building permit was actually granted. Though you say that the house is being “legalised” – on the basis of an architect’s certificate saying the house is 4 or more years old? So maybe there never was a building permit granted 10 years ago?
However, regardless, it is somewhat foolhardy not to comply with basic fire regs requirements, You are the purchaser and so hold all the cards so it is something you can insist on being rectified. Or knock the cost of it off the purchase price!