I am not a big fan of ‘weasel words’. In a perfect world everyone would be conscientious and do a good job at every stage, however when asked by the Client to produce an official sign-off of ‘all the works’ it helps to have some words which cover most eventuality and has been looked at by some risk adverse people far smarter than you or I.
So here is a statement which you can re-use in your sign-off:
“In so far as ascertainable in performing our appointed services and subject to the terms of our appointment, we confirm that the works appear to have been designed & implemented in accordance with the building contract between <<CLIENT>> and <<CONTRACTOR>> dated <<DATE>>. This statement is for the sole use and benefit of <<CLIENT>> and may not be relied upon by any other party.”