When you upload your package with dput, you can use to -f option to force the upload if the same version already exists on d-mentors.
ah! good tip!i'm used to Ubuntu PPA's where you can't do that (i don't think... i think if you -f it rejects them).
OK, the package is now available from: https://mentors.debian.net/debian/pool/main/f/flatbuffers/flatbuffers_1.3.0-1.dsc with thanks jonathon