A "miscalibrated" spot meter!? So you're thinking it might have been trod on, chucked around, dropped, left out int the sun...?
True, digital spot meters (or incident/reflective/spot/flash meters) do have the provision to be calibrated based on lengthy, proven experience by the photographer to a specific situation (my own is calibrated to +0.5 baseline),true also, they can be reset to factory defaults, if that will put you at ease. Old style analogue meters are not a reliable investment given their primitive measurement devices that do deteriorate over time. A rudimentary test of a spot meter (or all functions of a hand-held meter) would be to use alongside a reliable SLR, also with spot metering e.g. Olympus OM4, any one of the high end Nikons etc. The readings do not necessarily have to be identical but they should be close measured from the same position and looking at the same place.