Thank you, all, for your replies.

As suggested, it looks like there is little to do but correct each style that is experiencing an issue I am having where all the bolded Arial text now appears as plain (and shows as "Arial Bold (headings)" in the font drop-down. As pointed out, though, I can at least shorten this task a bit by identifying the "top-most" style that is referenced by others and fixing that...it should cascade down through the inheritance chain.

I don't know why this suddenly happened to everyone at my company; maybe a Word update or something.