Yes, but text/tab-delimited-values/.tsv is older.  .tsv dates from the days of Gopher, but text/csv was formalized only in October of 2005.  Presumably nobody has asked for it before, for some odd reason.

Now we get to debate again whether updating mimetypes with a registered type can be considered a bug fix.  We've gone both ways in the past, as far as I can tell.  This one has the advantage of actually having a formal IANA registration, unlike the last couple.