>Hi Martin:
>
>>Do you mean taking the date of the data file to determine the corresponding decade? I wouldn't consider that to be any assurance, but if you want...
>>
>Why do you consider that unreliable? Would that be the date the file was created or processed?

On the machine where it was created, sure. But you can't really be sure if the date was changed during the transport to the machine you're using it on. Many utilities which transport the files may affect the file dates - and I've even seen impossible combinations of last accessed/updated/created dates on system dll files. So these file dates are a sort of indicator on the possible age of the file, but not 100% reliable.