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But translation is contextual and "Issue" comes up in only one context in Zotero: as the issue of an academic journal. I'm pretty sure that's almost always "Número" -- I don't think I've seen ejemplar used for this in any metadata/citation context? Browsing dialnet, e.g., I see versions of this throughout Año 2014, Vol. 17, Número 2 (from https://dialnet.unirioja.es/ejemplar/372648 )
Indeed ! I don't have a handy link to the rule book (my old printed version, Bibliographic Description Manual (7th revised edition - 2008) is all I could find) but I know that for literature database and cataloging purposes the word issue=número. At least in the guidance for LILACS Literatura Latino-Americana e do Caribe em Ciências da Saúde (Latin American and Caribbean Health Sciences Literature).
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But translation is contextual and "Issue" comes up in only one context in Zotero: as the issue of an academic journal. I'm pretty sure that's almost always "Número" -- I don't think I've seen ejemplar used for this in any metadata/citation context? Browsing dialnet, e.g., I see versions of this throughout Año 2014, Vol. 17, Número 2 (from https://dialnet.unirioja.es/ejemplar/372648 )
Scielo also seems to use número: http://www.scielo.org.ar/scielo.php?script=sci_alphabetic&lng=es&nrm=iso