Well, to understand this, you have to understand that it involves the old "Texas brag" about how everything is bigger in Texas. When it comes to claiming a musician as a "Texas musician", the boundaries of the state certainly get a lot bigger :-)

Of course it seems fair to count anyone who has made all their recordings while living in Texas in this group. But, in addition, musicians who grew up here but left to become famous elsewhere seem to get included (Ornette Coleman, Sunny Murray, Janis Joplin, Steve Miller, ...) and I don't think anyone bothers to poll them on whether they still consider themselves "Texas" musicians.

In addition, if someone from Louisiana or Oklahoma become popular, they've probably done so only after substantial time on the road in Texas. So who's to say that Bob Wills isn't really a Texas artist anyways? Hey, we'll even claim New Mexico artists if they let us.

Then there are the folks who live in Texas for a while and then leave. Lucinda Williams did not release any recordings during her Austin tenure, due to record company hassles, but I've seen her listed as a Texas artist. And what about Ian McLagan and Iain Matthews? Despite spending most of their careers in Great Britain, they live here these days, so it seems only fair to claim them, too.

And of course Guy Clark and Townes Van Zandt are thought of as "quintessential" Texas artists even though each of them left Texas in the late 70s.

What it boils down to is this:

We claim 'em as Texas musicians if we like 'em. And, in these days of increasing homogeniety all across the country, who can really complain if we're trying to keep the spirit of the Texas Brag alive?