Azed - Last 2

[JJ109]

20a Speaker in dialect dialectologist eventually grasps (6)
STE _ E _
12d Chamber choir plus one judged to include contingency (9)
SE _ E _ T _ EN

The last letter of 20a is the 5th letter of 12d
I have answers for these but can't parse completely, but there are a few alternatives, none of which seem to fit together. Many thanks

NB Azed uses a lot of dialectic and foreign meanings that you haven't heard of and have to look up.

[fiction-factory]

Steven?

[goodgoalie]

20a Steven (hidden)

[fiction-factory]

I just suggested Steven because it's hidden in the clue, but clue seems too convoluted to be that

[JJ109]

Thank you - I can't believe I missed that.
So why is it seventeen ?

[goodgoalie]

Chambers has Steven as: 'a voice (now dialect)'

[goodgoalie]

The chamber choir is The Sixteen, often conducted by Harry Christophers:
https://thesixteen.com/

[JJ109]

and of course judged = seen, and event = contingency
Many thanks

[JJ109]

Many thanks to both of you, FF and Goodgoalie
I hate not finishing them!