I'll be damned - good to know and appreciate the correction! I couldn't figure out their policy a few months back as we had a group traveling to STT with one person looking at JetBlue and they couldn't figure it out, either. I called customer service and was told after consulting with a supervisor that they don't allow PFD cartridges in either checked or carryon. JetBlue doesn't spell out the exception on either permitted/prohibited baggage policies for whatever reason.

Still not sure how airlines would even be able to enforce additional restrictions beyond TSA's exemptions - it's not as though they are rifling through bags after the security checkpoint.