The Bright Star Monitor systems primarily perform survey monitoring observations, but there are some overlap fields. For example, they use the same Landolt standard fields. On occasion, you can run across a sky location using Seqplot where results from both BSM-north and BSM-south are available. One such star is located at
20:42:33.85 +00:16:02.3
The results:
System V B-V V-Rc Rc-Ic V-Ic
BSM_NM 12.200 0.686 0.384 0.352 0.733
BSM_South 12.204 0.683 0.389 0.349 0.732
APASS 12.208 0.685
where I haven't converted the g'r'i' of APASS, but just used those filters that are the same. The formal uncertainties on these measures range from 0.02 to 0.05. So you see that it is possible with transformation to have agreement between very different systems (north/south, colored glass vs. dielectric filters, refractor vs. reflector, etc.).
Arne