Sarah, I'm in Houston (and I learned it with "Nueces", too). Somebody tried to squeeze "Nacogdoches" in, instead. "Nacogdoches" is long enough to be its own verse, isn't it? Oh, well.
Of course, the versions of songs we sing now are not as they were sung then (as in the case of Soldier's Joy). People forget or mis-hear pieces of lyrics and fill in with what makes sense to them, and they often don't have the historical knowledge or concern to make sure it all checks out (not a criticism--I'm as in danger of doing this as anyone, and I'm sure I sing inaccurate lyrics all over just because I don't know any better). Since people can still be forgetting and mis-hearing 150 years later, anachronisms aren't really surprising.
Neither are regional inaccuracies, since not everyone has seen the places they sing about. I wouldn't intentionally WRITE a song that was inaccurate, but I might perpetuate it out of ignorance. "Streets of Laredo" often includes lines about "I was born in southeast Texas, where the lilac does bloom and the gulf waters flow". Lilacs cannot grow in southeast Texas (I'm not sure they can grow ANYWHERE in Texas). They probably mean azaleas, oleander, or crepe myrtle, and I wouldn't be surprised if those were introduced from somewhere else as decorative plants (any botanists in the house?).