The best way to guarantee long-term access and usability of data is to store it in standard formats that most software programs are capable of using.
Most modern software applications are able to access data created in previous versions and by other, competing applications. However this can't be guaranteed so the safest course of action is to use open or standard formats instead of proprietary ones.
So, for example, we will not accept proprietary Microsoft Excel spreadsheets. We ask depositors to convert such data to an open format such as comma-delimited values.