You I&T to the current BS 7671, so just now you (or your customer) have a choice. Whether what was compliant then, but no longer is now, is a C3 or C2 depends upon how out of date is the installation.

What the landlord does with the EICR is his business, not yours.

Yes but as I see it (others may disagree) the 18th Edition solely is mentioned in the Landlord Law then it prohibits the 19th when it comes in ounless parliament changes it or there is permission in place to allow the  Secretary  of state to vary it.

At the very least, you follow the test procedures in the current edition. So for example, you test RCDs at 1 x IΔn AC only.

I don't see any practical difficulties because items which were compliant, but no longer are would be coded C3.

I don't foresee any backward steps, but if for the sake of argument, the 19th Edn prohibited protective bonding, you might still award only C3. If C2, it would have to be disconnected, so I don't see a huge practical problem.

In any event, there will be a civil servant somewhere who will be keeping an eye on things.

The law explicitly says that the property must comply with the original edition of BS 7671:2018 at all times (it even quotes the ISBN number) - not any amendment. The law says nothing about what the I&T should be to: that is purely down to agreement between the landlord and the electrician - of course in the absence of any formal agreement, a landlord might reasonably assume the electrician is doing the "right thing" - and that usually implies inspecting against the current (amd2) edition of the regs.

Since it is a statutory instrument, it's supposed to be up to the relevant government department to keep it up to date, with the SoS signing it off and parliament giving a token nod. In practice, SIs are notoriously unmaintained - look at ESQCR, which still thinks properties are wired to BS 7671:2001 amd 1

The law explicitly says that the property must comply with the original edition of BS 7671:2018 at all times (it even quotes the ISBN number) - not any amendment. The law says nothing about what the I&T should be to: that is purely down to agreement between the landlord and the electrician - of course in the absence of any formal agreement, a landlord might reasonably assume the electrician is doing the "right thing" - and that usually implies inspecting against the current (amd2) edition of the regs.

Since it is a statutory instrument, it's supposed to be up to the relevant government department to keep it up to date, with the SoS signing it off and parliament giving a token nod. In practice, SIs are notoriously unmaintained - look at ESQCR, which still thinks properties are wired to BS 7671:2001 amd 1