Nice job, that makes me think if same models sound identical when leaving factory.
Of course they sounds different, the only question is to what extent. If we, for example, compare two modern conveyor amps made in the same day or week, they may differ just slightly. But if we compare any couple of amps of the same model with an issue date difference of several years, the contrast in sound may be as large as if it were completely different amps. And the old stock one will most likely be better, but it is impossible to guess for sure.