The PIR or Electrical Installation Condition Report as it's now called is somewhat limited in the checks carried out. In the main the inspector is looking for DIY blunders. He does both a visual and a meter based test both complimenting each other.
There are some items which are pass or fail continuity of ring main, earth loop impedance, insulation resistance are examples of go/non go tests and to not find fault where it exists with these is easy to see and condemn where missed.
With the visual part one looks at general condition and according to what extent the test is agreed will maybe remove 20% of the sockets/connection units. If no faults found it then stops. If a fault is found then the items tested will increase. At some point of course a rewire would be recommended at which point inspecting and testing stops.
The cost to remove every socket and connection unit would be prohibitive so there has to be an agreed limit to the tests. It is very rare for any house to get a clean bill of health in fact most testers hunt for a fault as once any fault is reported then they can say that they stopped testing considering it would be retested once the faults are corrected.
The report was split into four categories now reduced to three which report
guide here and
here so we have.
1) Dangerous.
2) Could become dangerous.
3) Recommended to be improved.
The first two remain but before it was:
4) Does not comply with current edition.
3) Can't be tested. For example where one would need to break seals.
So where for example the colours are red black and green rather than brown blue and green and yellow with a modern report there will be nothing reported.
The idea is to only report items really needing attention as to fill the report with silly items likely means whole report is likely disregarded.
So to get a report with no items high lighted is very rare. So first question what items were high lighted? Second question were any of the high lighted items connected with faults found. i.e. would it be likely the report was not detailed as it recommended corrections which once completed would have redressed the fault.
OK there are bad electricians who miss testing items but most electricians are clever enough to leave them selves a get out of jail free card and will find some fault which once corrected would mean some one else would have to had tested it.