What you are describing does not sound like an EICR (probably called PIR {Periodic Inspection Report} back then) but, rather, an EIC (Electrical Installation Certificate) just for the consumer unit change.You are right, the certificate was for 'Change consumer unit and test', ie a brand new consumer unit. But the circuits pre-date the new consumer unit by many years, yet they are covered by a 10 year certificate for replacement of the consumer unit.
As I've recently written, I don't really understand why that (or any other) certificate should influence an insurer's policy as to whether or not they are prepared to insure a property which (currently) has PVC wiring in a thatched roof.
Kind Regards, John