I don't know if I'm going to use this pattern again, but i would appreciate fitting comments anyway: that's great to improve oneself, I think

It looks a bit loose in the waist, to be honest - there's a bit of ripply stuff going on that I think would go away if you had it just a hair snugger. Even an inch off might help.

I know... the problem is that the mock-up was right, but when I did the real thing I had all the cording to consider and there are pieces that simply haven't room at the waist for a 7mm boning because of the cording, so I had to give 1 or 2 mm here and there to be able to put the boning in.
If I had noticed the fact beforehand I would have reduced a little the cording, especially in the three front panels OR (probably the best solution) I would have chosen a 5mm boning.
It was SO frustrating.....
The only way to fix it now would be to unpick all the front seams and reduce boning channels for a 5 mm boning (which I don't have, by the way)... I don't know if I have the fortitude to do that

Fair enough. These things happen, and it's a lovely piece of work in any case.

The pretty housemaid corset was a Symington design and one of the things that I read about Symington corded panels was that the cording used was twisted paper. Depending upon the final application the cording could have been composed of up to 3 layers of paper. The paper went through a water bath, was twisted, and then sewn between two layers of cloth in a long continuous loop. Some of the machines described had six needles; could sew corded panels with 6, 12, or 18 rows of cording since the strip was a continuous loop. The loop was then steam dried and the cotton would shrink around the paper cording. Corded panels were then cut and used in the corset.

If you think paper cord is a strange material to use you haven't seen high quality paper cord. Single layer tightly twisted paper cord is extremely strong.

There was a museum publication about the Symington Collection and this bit about the cording appeared in the publication with a picture of the cording being sewn.