Does replacing the sail window break rule compliance?

So, have this old training sail that I am about to sell for €150...

Before selling it, I wanted to repair the window decently because it had a bunch of holes sealed with tape / adhesive Dacron. A sailmaker advised that the only way was to replace the entire thing, so I trusted him and let him do his job.

Now I post an advert online with details on the repairs made, sail status and usage... and someone replied saying that now the sail is no longer class legal...

Now, I strongly doubt...

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