'Opus A #B' or '#B Opus A'?

[allchopin]

This question may be a bit pedantic but I would like to know for sure.  Dealing with a piece with and Opus number and an order number, which comes first in the title?  I have usually said, for instance, Nocturne #2 Op. 55.  But this really isn't the second Nocturne he wrote, so would it go after Op. 55?  To indicate the set number?
What's the deal with this...

[ayahav]

Opus A No. 4

(we use No. rather than #).

You can even think of it as a possessive

Op. 55 No. 1
   is the same as:
      Op. 55's No. 1

[Hmoll]

You can even think of it as a possessive

Op. 55 No. 1
   is the same as:
      Op. 55's No. 1

I've never seen it as possesive in English.

I'll try  to  keep this short, and not turn it into a "Bernhard Special" (I mean that with all fondness, Bernhard).

Using Beethoven sonatas as an example (because I can never remember the opus and #s of Chopin nocturnes) there can be three numbers to consider: a) the number of the sonata out of his 32, b) the opus#,  and c) the number within the opus number.

For example, I have seen people write "Beethoven piano sonata no. 6, in D Major Op. 10 #3. I think that is a little confusing. Better would be Beethoven sonata oin D Major op10 #3.
Maybe it's me, but I think "Beethoven piano trio #1, Op. 1 #1" looks strange.

To further complicate things, I suppose you could say "Chopin etude # 14, Opus 25 #2," but I don;t like the way that looks. "Op. 25 #2" is fine.

[ayahav]

It isn't used as a possessive, but it's a way to remember why the number is before the opus - because the number is a sub-category of the opus.

[Hmoll]

OK, I get it.
I though it might be possessive in one of your many languages.

[allchopin]

This question then lends itself to the key of the piece- does it go before or after the Opus and No. ?  Because every piece in my 2.x gb classical directory of music is named incorrectly (should take care of my weekend...  :-/).