Just checked that several other pure BOINC project i run sweep the complete results more or less the day after. WCG keeps them 4 days after quorum was achieved. Including all the 'in progress', 'pending', 'inconclusive' work, probably 1 - 1.5 million WU records are kept on show. No idea how in volume this compares to other DC projects.

If u want to see detail record of what your machines crunched over a longer period, set up BOINCview and hook it up to all the machines. It automatically tracks all work in progress and has a separate tab for all finished work. Run times, dates completed, state of completion are recorded. It does not record the claimed credit... was asked for and rejected.