I've compared a few available XSLT stylesheets from standards/marcxml/xslt .
As it noted in A Repository of Metadata Crosswalks, the transformation from MARC XML to Unqualified Dublin Core 1.1 is realized in three encodings, requiring three separate XSLT scripts: as OAI DC(MARC21slim2OAIDC.xsl) , as SRW DC(MARC21slim2SRWDC.xsl ) , and as RDF DC(MARC21slim2RDFDC.xsl).
I've noted that YAZ Proxy download has slightly different (and seems older) versions of the similar stylesheets.
The most notable difference is that MARC21slim2SRWDC.xsl output doesn't include namespaces,e.g shows <title> instead of <dc:title>.
Also seems that MARC21slim2SRWDC.xsl has more updates and produce nicer output, e.g. uses normalize-space Function.