I think I have got it. The special upload form may not be as simple as last year [1] with a field for Rijksmonumentnummer. For Germany, i.e., the user should first select country, state, municipality, and then type the number, unless the identifier includes some codification. For Spain, if all monuments have the same prefix R-I-51, then this part is not relevant as an identifier and it will be easier to type only the integer part.
[1] http://commons.wikimedia.org/w/index.php?title=Special:Upload&uselang=nl...
Vicenç Riullop