I am an NICEIC approved contractor, HMO developer and HMO Landlord. You may find that your limits on the domestic installer scheme have been reached on this type of alarm system. The NICEIC domestic installer certificates are not available for this category of system. Looking on the NICEIC website specimen paperwork section there are no fire alarm installation certificates for domestic installer, these are only provided to Approved contractors on red paperwork.
HMOs are an anomaly, they are domestic properties with commercial features, such as CAt A alarms and emergency lighting etc. So they are domestic but only on the house wiring itself everything else is classed as commercial by the NICEIC.
Generally 2 floor student HMOs are mains interlinked LD2 whilst 3 floor properties are full cat A fire system. Full fire systems are not as straight forward as you might imagine. It still all wiring and codes of practice, but you cannot account for knowledge of where to place alarms to avoid false alarms or even what make of equipment will give you less false alarms.
I am an electrician that tests alarms (and fits them) I see many alarms that have been fitted by electricians that are not quite right as it isn't their main type of work. The nuts and bolts of fitting them are there but they miss out things or don't fit them quite right as they don't know the regs and a badly fitted fire alarm can give false alarm headaches like no other for the landlord. I have been to some HMO houses that the alarm has been going off 5 times a week!
As Anthony said you need to fully absorb Pt1& Pt6 of BS5839 to get up to speed. Then read as much technical advise as you can from this forum and other sources. Like everything it is absorbing all of the detail that matters.
You need to check with the NICEIC first though if you decide to crack on, just to make sure you have the defined capability on the domestic installer scheme, as all councils require full alarm installation documentation, which they will expect to be on NICEIC paperwork.
As for the council drawings not showing call points they should. Never been to one yet that hasn't!! What may be happening is that until the enforcement of the latest HMo housing act a year or so ago most councils didn't have an active HMO policy. Most council enviroment depts are not prepared or up to speed with the legislation and are vastly understaffed and underqualified for the job. I work in swansea, where HMO has been heavily enforced for 20+ years. Council is precise with everything. Cardiff who had no previous enforced policy on the other hand is a shambles and have no clue and admit it! what installers have to be careful of is fitting substandard fire systems, firedoors etc to properties looked after by learning councils, because in 5 years time when they are reinspected and they are more up to speed it will be rip put time. I have seen it happen!
Hope this helps.