I categorize them by setting instead of order. Some are in Cabot Cove, some in New York, some on vacation spots like London or the Caribbean. When I'm in the mood for small-town New England charm, I pick a Cabot Cove book. When I want a travel mystery, I grab one set abroad. This thematic grouping is a more meaningful way to choose your next read than a arbitrary number. It matches the mood you're in.
I find the publication order fascinating as a cultural artifact. Reading from 1989 to today, you see how the genre's tropes and societal attitudes shift subtly. That's a cooler project than forcing an in-universe timeline. Read them to see how the cozy mystery adapted over time.