We did have a bunch of patches to actually make a lot of builds reproducible, but integrating changes like that has been pretty slow. I'm pretty sure a lot of these patches have since been adopted, pulling things much closer to bit-by-bit reproducible.
Unfortunately there's no real metric we have to keep track of that at the moment, like Debian ("%XY.Z are working"). But it looks like basically all distros are finally starting to converge on this.
There was no intentions to claim you where not working towards reproducible builds. I have come across several people that conflate what NixOS offers, and what reproducible builds are.
However, great that you have been working towards this! Arch Linux has been cooperating with Debian and currently build our packages on their infrastructure to produce graphs and test our packages. I assume NixOS can do the same thing if the manpower is present.
Unfortunately there's no real metric we have to keep track of that at the moment, like Debian ("%XY.Z are working"). But it looks like basically all distros are finally starting to converge on this.