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.