Given the explicit requirement of BS7671 for these devices in care homes, high rise residential buildings, student accommodation and HMOs, will fire risk assessments of such premises acknowledge their absence in existing buildings within this group? 
I ask because many in the electrical installation industry do not share the view that these devices are an effective means of reducing fire statistics where the ignition source is electrical in nature. 
Quite apart from the view of whether they actually function, there is no sufficiently detailed body of fire statistics that could be referred to in order to form a valid opinion. 

Since no one has yet replied......?

(Just my opinion)

AFDD's only became a "must" in March 22, anything installed prior to then will NOT require an AFDD

To confirm a site has AFDD's you will need to open the consumer unit lid (That's lid, not cover) Should you really be going that far? What will you then do if none are installed? As I said prior to March they need not have any, so your first problem would be you need to establish when the consumers unit was installed. Suppose it was installed last week in a care home and it has no AFDD's all you can do is point out it should have them but doesn't have them when you looked.

I would also suggest that a lot of places will not have them purely due to cost, one single AFDD costs £100* which is ten times as much as an RCBO also anywhere that "must" have  AFDD's will require one for each circuit of sockets*, and they are known to NOT WORK 100% of the time on final ring circuits*, and since most sockets are on ring circuits...........

Give it another 5+ years and the price comes down then yes, but until then.......

* I checked on manufacturer's website.

Thank you Green Foam. The reason I ask is to get the perspective of a fire risk assessor. The intent of the regulation is to guard against ignition sources from appliances rather than from the fixed wiring, otherwise why would they be required only for socket outlet circuits? The regulation also sees the risk as a life safety one as the situations where AFDDs are required are demonstrably ones that have difficult conditions in terms of evacuation in a fire. 
So the conclusion must be that these devices are regarded as an important aspect in mitigating the risk to human life from fires that have a source in electrical appliances that are connected to socket outlets. Surely that is exactly the sort of thing a fire risk assessor should be considering. It is irrelevant as to when the devices became mandatory as far as BS7671 is concerned. Buildings probably pre-date many basic fire control measures but that doesn’t necessarily mean that the building need not have them.