I would like to know how you would handle a commercial EICR with a BS5839-1 system installed
Also how many BS5839-6 systems have you coded with a C1 or C2 while doing EICR's
TBH a lot of these videos are not worth a watch and are not even worth the bandwidth they take up
In answer to your question; none because I have yet to undertake a single one and so it's all hypothesis until such time I'm competent enough to under such works.
Grade F system (battery only - Fixed or replaceable), if any detectors found to be dead then I would C2.
Grade D System where, mains is present and working bit alarm is past battery expiry date I would C3 if other detectors were on the same level, otherwise if the next functional detector is above/below the current level then I'd C2 as you're losing the early warning that an alarm on the same level provides.
If the same system (Grade D) had faulty mains but working battery, again I would C2 or C3 depending on any 'local' backups.
MIs would also influence the coding as the BS EN standard would dictate exactly how that alarm should perform on mains and/or battery and if that manufacturer can't guarantee if Thier items will work with 1 or the either power sources missing.
With regards to -1 systems, in comparison with -6, I would code along a similar vain, I would also pull on the FSRRO and cite from that as you're then talking statutory duties, as opposed to a non-statutory product standard. You'll find they tend to sit up when you start bringing EAWR/FSRRO into your report as THAT is what most commercial/industrial entities will be familiar with, most tend to have a dedicated SHE manager or department, which if any good, would welcome your forensic analysis of not only BS7671 but also any overlapping 5839/1838/5266 observations.
That's me anyway, probably over the topby some judgements bit I'm satisfied with it.