No one seems to want to touch this, so I'll chance my arm. I think you're right, and that "sobrecartar" means reissuing a previously issued court order or injunction, or, in this case, notice. It sounds as though it was first issued and sent without a document that should have accompanied it, and that the correct procedure is to reissue it with the missing document.

"sobrecartar" is translated in Neuman and Baretti's nineteenth-century dictionary, and in a number of other places, as "to repeat a former injunction"
http://books.google.es/books?id=RSASAAAAIAAJ&pg=PA636&lpg=PA...

Here is a Bolivian court judgment that turns on the meaning of this word:

"Para una debida comprensión del término “sobrecartar”, se tiene que, según la definición expresada en el Diccionario Enciclopédico de Derecho Usual de Guillermo Cabanellas, es un: ”nuevo mandamiento judicial por no haber tenido cumplimiento el primero”."
http://www.tribunalconstitucional.gob.bo/resolucion12792.htm...

So you could say "so that it can be reissued to us", or however you want to phrase it.

Here's an example of "reissue" in English:

"The court may, upon the filing of an affidavit by the applicant that the respondent could not be served within the time required by statute, reissue an order."
http://statutes.laws.com/california/wic/15657-15657.7