uax uts dutr?

[Marco . Cimarosti]

Out of curiosity, when did the acronym "UTR" ("Unicode Technical Report")
mutate to those "UAX", "UTS", "DUTR" that I see in
<http://www.unicode.org/unicode/reports/index.html>? 

And, BTW, how is it that a "Superseded UTR" is not, say, a "SUTR"?

_ Marco