Yes, I agree it's very strange that San Cayetano does not figure in the postal address. The postcode 30700 seems to be a general one covering Torre Pacheco, Hortichuela and San Cayetano. Maybe the last two digits of the postcode will change to make it more specific when the site is fully recognised.
San Cayetano used to have under 1000 inhabitants, so maybe it didn't need any more than that. You could always substitute San Cayetano for Torre Pacheco if you wanted to make it clearer.
We have family in Ireland and their address is just the name of the village, but the postie seems to find them OK.
Not much help, I know. Sorry!
Diane