The ordering of the CCD vertices is different for BASS, MzLS and DECaLS. For each individual survey, the CCD corners are ordered as in the table below, in which RA increases to the right and Dec increases upwards.
In the table, 0 denotes [ra0, dec0], 1 denotes [ra1, dec1], 2 denotes [ra2, dec2] and 3 denotes [ra3, dec3]. The quantities ra0, dec0, ra1, dec1, etc. are defined in the data model for the ccds- files on the files page.
Note that for 2084 MzLS exposures the column ordering is reversed. These exposures were taken when the telescope was pointing at hour angles (h.a.) of more than 6 hours; specifically at locations beyond the great circle that passes through the north celestial pole and the points Dec = 0, h.a. = +/- 6h.