Who did my great-great-great-grandfather marry?

Question

I can say that my interest for genealogy started when I got my great-great-grandfather baptism record from Ciudad Real, Spain. This is the record (online version in Family Search):

It's a bit hard to read, but the following information can be extracted from it:

• Juan de la Cruz Alejo
  • Father: Juan Antonio Alejo
    • Grandfather: Antonio Alejo
    • Grandmother: María García
  • Mother: Carmen Campos
    • Grandfather: Baltasar Campos
    • Grandmother: Juana Ruiz

Carmen Campos and her parents were born in Elche de la Sierra in the province of Albacete, Spain. The marriage of Baltasar Campos and Juana Ruiz (who is, in fact, Juana Moreno Ruiz, being Ruiz the second surname) is documented and I also have the baptism records of all of their children, including Carmen's, born in 1827.

The problem is... that I also have her death certificate from 1828. Carmen died being less that nine months old.

So evidently my great-great-great-grandfather Juan Antonio Alejo did not marry Carmen... or did he? Who did he marry? I have thought about the following choices:

• Baltasar and Juana had another child after 1827 and gave her again the name of Carmen. But I can't find any record of her. In fact, it seems that Carmen was the last child of the couple.
• Juan Antonio Alejo married an older sister of Carmen's, but she told him her name was Carmen (maybe she changed it after Carmen's death). There's a couple of them who did not marry any other person who can be candidates.

But now the next problem is... that I cannot find anywhere the marriage record of my great-great-great-grandfather Juan Antonio Alejo and whoever he married in the Campos family, as I expect that record to contain the real name of Carmen or at least confirm that he married a Carmen. Juan Antonio was born also in Elche de la Sierra, he first married María Parada and they lived in Riópar, Albacete, until something happened between December, 1846 and January, 1847, when María Parada and two of their daughters died. It seems that Juan Antonio then moved to Ciudad Real, where he met Carmen Campos, supposedly married her and had a legitimate child, my great-great-grandfather Juan de la Cruz. I tried searching for his second marriage record in Ciudad Real, Elche de la Sierra, Miguelturra (quite close to Ciudad Real), but I got nothing so far.

So:

• What possible theories do you consider more plausible about who really was that Carmen Campos who married Juan Antonio Alejo?
• Any tips about how and where can I find Juan Antonio and Carmen's marriage record?