Sometimes it's legal issues at the heart of it, but this is mostly with respect to records as opposed to documents (e.g. procedures). I suspect this is where the confusion comes in within this thread - most folks saw DOCUMENT instead of RECORD in the original post.. I go into some detail about the distinction between 'documents' and 'records' in my Implementing ISO files set.
With either records or 'documents' - if one of your procedures says you're going to keep a specific document (or record) for a specific time and then you will destroy it you are bound by your procedure, not ISO. As I said - I haven't seen this used with documents (destroy by date). It is extremely common with records.
Most companies keep certain records for a certain time. Some records are kept for legal reasons (for example in a transportation, copies of drivers logs are kept for a certain period of time by federal law). I have seen some smaller companies that had 30 or 40 years of records, to the extreme.
Now - why the big deal if you keep it longer than you say you will? It's not a matter of logic. It's a matter of how you wrote your procedure. If you say you'll do this you don't have a choice. You can avoid this if your procedure is worded along the lines of defining a minimum retention time while stating that there is no maximum retention time.
> Do we have to have evidence of records already disposed, I
> mean like a sheet that tells when a specific record was
> destroyed or something like that?
Not that I am aware of.
> it is probably prudent to maintain records of disposal.
This is a good idea in some companies. In others it is vast overkill. If you're a manufacturer of medical devices this is probably more important than if your company injection molds toy dolls for Cracker Jack boxes.
Beky - If you're talking ISO, reword your procedure for the disposal of quality records and get on with life. If you are QS the extended requirements take precedence and require that you define a destruction method and timeframe. The sheet is not necessary as evidence. The absence of records beyond the specified time is your proof. However, again I caution you... Each company is different. Make sure what you do is appropriate for YOUR company.