I would agree the inspector could select a different time period, however the standard was 10 years maximum and common to see stickers on a fuse box or consumer unit saying test due with a date 10 years from the last test.
It is also permitted to have a continuous testing system, most companies I worked for would be tested by room or distribution board, we used the LIM code to say how much tested, and we would often have two visual only (inspection) between each testing and inspecting, the HSE could tell us we were not doing it enough, to I have been involved with many HSE visits and that has never been raised.
Until new law only workers needed protecting, however few homes don't have some worker in them. So my mothers house had to be to standard as she had carers visit, they are clearly working, so although house did not need to be to a standard for mother, it did for carers. Be it meter reader, doctor, nurse, gas man, or other tradesman, it is rare to find a home which does not have some one who it is classed as their place of work.
We did work under "Electricity Safety, Quality and Continuity Regulations 2002" and "The Building Regulations 2010" and the "The Electrical Safety Standards in the Private Rented Sector (England) Regulations 2020" refers to the first two with some of the definitions.
So the landlord must ensure that the electrical safety standards are met during any period when the residential premises(2) are occupied under a specified tenancy; and ensure every electrical installation in the residential premises is inspected and tested at regular intervals by a qualified person; and
regular intervals” means at intervals of no more than 5 years.
He must obtain a report from the person conducting that inspection and test, which gives the results of the inspection and test and the date of the next inspection and test, and supply a copy of that report to each existing tenant of the residential premises within 28 days of the inspection and test.
Which all seems good, however although it says “electrical safety standards” means the standards for electrical installations in the eighteenth edition of the Wiring Regulations, published by the Institution of Engineering and Technology and the British Standards Institution as BS 7671: 2018 it does not say how this report should be presented, only that must be done by “qualified person” which means a person competent to undertake the inspection and testing required under regulation 3(1) and any further investigative or remedial work in accordance with the electrical safety standards.
So I could be asked by a landlord to visit some premises and tell him if there is anything obvious which needs doing, I could send him a text saying "Looked at no 59 it seems OK, did a quick check of loop impedance with plug it tester all seems OK" and he could forward that text the tenant, and until there is a court case, and case law is generated this could be seen as complying with new law. And if I had done a full EICR say 6 months ago before the old tenants moved out, this would be likely considered as being enough to satisfy the IET requirement that homes should be inspected and tested when new occupants move in.
In other words the law is so wide open, it is easy to get around, we all know any health and safety report should be in writing, so a phone call is not good enough, but a text message is.
Now if the new tenant says I have noted holes in the consumer unit where no MCB's has been fitted and asks does this comply one can say no, we know 12.5 mm is the maximum allowed and a MCB is wider than that so it fails, but re-wired 2016 so likely does not say it needs testing before 2026 even if the new rules over ride that, but it would seem unlikely there is a need for more work to be done so soon after a re-wire.