In the AAVSO Target Tool, there are often stars that have values like:
17.0 p 12.5 p
for the min and max magnitude. What does "p" mean in this context? I can't find it in any of the standard photometric systems.
p stands for "photographic".
These values usually come from old photographic plates and are close to the Johnson's B passband.
Then you will find that these ranges are usually a couple of magnitudes fainter than visual for red variables.