While an EICR is not retrospective the PRS clearly uses the 18th edition as it's reference point for electrical safety, so should the EICR reflect that when deciding on what codes need to be applied or the satisfactory / unsatisfactory condition of the installation. My take on the PRS legislation was that it was intended to improve the electrical safety of properties in the rental sector and without any C2's it will not achieve it's intended aim as C3's can sit on the report forever and a day with no action needed to improve what maybe considered problem areasAn EICR is not retrospective… so it doesn’t matter if it’s 5 or 15 years old regs. (Or 50 for that matter)
From a legal point of view as with most things there will be no precedent set until someone dies and the legislation is tested by an inquest and then the finger of blame will be pointed amongst the parties involved and then no doubt other litigation will take place to decide who carries the can
From what has been posted by the OP it is difficult to take an overall view of the installation or the quality of the EICR but looking at the picture of the old Wylex board with some of the fuse base slots filled with silicone to prevent access to the live parts behind it rather than spending a few pence on proper blanks sets the acceptable level IMO very low from the letting agents side
From the OP I'm trying to understand who commissioned the EICR that the letting agent is downgrading as the way the OP reads it was the tenant that commissioned it which would then suggest there are some concerns about the safety of the installation