In theory if an installation was OK in 1970, and nothing has changed or degraded, then it is still OK today, the wiring regulations all refer to the design date.
However it is highly unlikely that the design has not changed. The simple thing is we no longer use tungsten lights, so we now have bulbs which can be changed while still powered up, as the temperature now allows us to handle them.
So if we take it to the extreme, if an inspector sees a EV parked outside, should he assume it is going to be charged from the 13 amp sockets, which will need therefore type B RCD protection etc?
I would say no, but point is if an inspector was to give a code C2 due to RCD type, we can't say he is wrong, we have the best practice guide, but it is only a guide, the only way to get a decision reversed is to go to the LABC or trading standards, there has been one case, but the electrician held up his hands and admitted he did not do a good inspection, had he held out, not sure what the court would have done.
I was myself worried about the result of missing faults, and I wrote a java script program to calculate volt drop, however realised the volt drop would need to be way out before an error could be proved. But the question is still valid in a way, if I miss a fault, and in 5 years time another tester finds a fault, which now requires a tiled floor to be lifted to correct, can the owner claim on me for missing the fault before the tiles were laid?
The simple watch my back method is to find fault, not really ethical, but if you find fault, some one has to repair the fault, and issue a installation or minor works certificate which post dates the EICR so I am in the clear.
I have watched videos of electricians removing all the down lights to check earth wires are present. And they are not too close to beams. This is not inspecting the condition of the installation, this is looking for installation errors. However in theory the installation and minors works plus previous EICR should be made available to the inspector. In commercial premises this actually happens, but my last house I had from new, built around 1978, and I was not given the installation certificate, it should have had one even back then, but until 1992 when the regulations became BS 7671 it was rare for any electrical paperwork to be raised for domestic electrics, and it was not until 2004 with the Part P it became essential to raise the paperwork.
And when my mother put the paperwork where I could not find it, I found getting a replacement from the LABC was near impossible, told would take 4 months, and would cost whatever time it took a worker to find it. So much for traceable records.
I had the same problem with calibration of a PAT tester, it turned out they could not trace the traceable records, and if I want to buy a house, I would want the paperwork to come direct from person doing the inspection, not vie the last owners who could miss out pages etc. I was caught out with this house, presented with the installation certificate, only to find it only covered less than a 1/3 of the house.
I have wondered what an inspector would do if I wanted to rent out the main house? It does not have a distribution unit of any kind in the house, that's in the flat below it. He has two options, either LIM or FI, unless he has assess to flat. He could turn power off, simply using the RCD tester would do that, but he could not turn it back on.
So the cover could be completely missing for the consumer unit, but that would be outside of his remit. The same often applies to commercial premises, even as the electrical engineer, I was not given assess to the step down transformer room, which I know had exposed wiring and did not comply with BS 7671 but did not need to, as under the control of the DNO.
) has 4 x 32A and 4 x 6A MCBs and 1 x 16A RCBO (hence an 'add-up total' of 168A) (and one currently unused 'spare way', occupied by a B32 - which, if ever used, would bring that 'add-up total' to exactly 200A), with a Main Switch rated at 100A. 
