if we remove a distro from the list of allowed distributions we have to be sure that there are no devices left on h-node that have been tested with that distro (especially if that distro is the only one used). Otherwise the system will alert that the distro is not allowed if someone try to update the page.
There isn't any list of the devices tested with a selected distro, anyway I think we could create such list (for example it could be useful to know what devices have been tested with, for example, Trisquel 4.5)