exact dates would require extensive google'ing :)

some approximates though:
dm14 - when q3 went gold, although it wasn't played until team abuse released tmp versions of some maps.
osp5 and osp6 - released with the osp mappack, some time after q3 went gold.
cpm4 - released with one of the cpm mappacks (i think), which was after the osp pack.
dm20 - introduced during ql beta.
dreadful place and purgatory - released some time after ql went gold.

Isn't dm20 one of the 'new' maps that the dreamcast version had?

Yea

technically true but kinda irrelevant cause it wasnt actually used in any mappool

That wasn't the question.

it was the question that i read between the lines, but you are right

wasn't there a Q3 map of dreadfulplace first?
http://lvlworld.com/review.php?id=2077

If the date in the readme file is anything to go by (12/2009), I don't think it had much of a life in q3. Seems like it was created for the contest alone. Which is where id got a handful of new the maps from.

dm14 was the first map, since its one of the original q3maps.
There was a special tmp version released that was played 2000-2001 or so. just like the one dm6 and dm7 had.
Still got them in my quake3 folder ^^

So many 'new' maps.