Hallelujah.I never didn't understand.
you proclaimed to want to help them as they were an old couple, so we have offered options as to what you could've done, some which would have helped by keeping the expense to a minimum to help you help the old couple, by your own admission you replaced the new board with a newer board so can only deduce that you charge the same for an eicr as you do for a full board change?
As has been suggested a plastic board installed at the time was reg compliant so therefore a simple confirmation with a satisfactory eicr would be sufficient?
But I suppose, providing your elderly customers were happy to pay then no harm done!