Thanks to everyone, especially Nava. Although I have read quite a bit about compound names, this is the first time anyone said straight out that Spanish does not have the concept of middle names. That makes a real difference.
My wife, Maritza del Carmen, has been abbreviating her name as Maritza C. since long before I met her. She told me that del Carmen was her “segundo nombre,” which I understood as middle name. (That’s what it says in Word Reference Forum.)
There was never a problem with it until she came to the U.S. and married me. We’ve had no end of problems with immigration, schools, social security, etc. Now I understand that there were not one, but three problems.
The first, of course, is the utter inability of the American system to handle Hispanic names, along with the incredible inability of most Americans to see any viewpoint that differs from theirs. The third, however was my own misunderstanding!
So, thanks again, everybody!