I found the problem. Something had corrupted part of the consolewd.ini file. I replaced it with a clean copy and that fixed things.
For anyone troubleshooting this in the future, the values used by Steel Gauges are in the customclientraw.txt file with tags ‘PressL’ and ‘PressH’.
When I tested with “known good” backup copies of the clientraw and customclientraw files, I forgot that those files get rewritten every time WD does an update. So, shortly after I copied the “known good” files they were replaced with current data containing the incorrect barometer extremes. Duh. Stupid me!
Thank you Mark for setting me straight on whether the Steel Series scripts cache values and Brian for pointing me to the consolewd.ini file!