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re: Debian Buster will only be 54% reproducible (while we could be at >90%)

Because of their design, binNMUs are unreproducible, see #894441 [3] for
the details (in short: binNMUs are not what they are ment to be: the source
is changed and thrown away)
To be specific, the source tree is extracted, then an entry is added to debian/changelog and then the package is built. This modified source tree is not retained.

It seems to me that binnmus could be made reproducible by storing the debian/changelog modifications in the buildinfo, then re-applying it at reproduction time.