It may be the case that the doors would not achieve 30 mins fire resistance when tested to current standards. However, isn't the whole gist of the current guidance that we should not be making decisions based upon whether doors conform to current standards - with the idea being that we make a judgement based upon whether they will be suitable within the environment in which they are located, and having taken into account the risks specific to the property.
Even if the door sets fail a modern 30 minutes test, would the effort and expense involved with replacing all of the (currently well fitting) doors be disproportionate to the risk? Would the availability of a alternative means of escape not be considered a significant mitigating factor?
It sometimes seems that rather than doing a risk assessment specific to a property it is easier to take the safe approach and suggest that anything which can not be confirmed as compliant should be replaced. However, my interpretation of the purpose built flats guide is that this approach should be avoided if possible.