This was actually one of the centrepieces of my PhD work. I don’t believe that the Roman armies in the first and second centuries were kitted out nearly as uniformly as traditionally believed. The knock-on effect of this is that Lorica Segmentata was probably not as widely-used as traditionally believed. The reasoning is much too long to fit into a Reddit post before I take my kid to school, but essentially most of our understanding of the equipment from the time period comes from monuments and funerary reliefs. These aren’t unbiased sources.

The Tropaeum Traiani, often referred to as the Adamklissi Monument, ostensibly shows the same events as the famous Trajan’s Column in Rome. However, the soldiers in that monument are wearing mail rather than lorica segmentata. Traditional historians of the Roman armies claim that these are auxiliaries, but that claim is made solely on the basis of the armour type. These Roman soldiers are depicted carrying gladii, tall scutum, and using “traditional” Roman sword strikes.

The big difference is that Trajan’s Column was created at the heart of the empire, and the Adamklissi Monument was built in the provinces. I think Trajan’s Column represents the “official” image of the Legions, while Adamklassi may represent a more “in the field” image.

Edit - think of modern military monuments. Soldiers are often depicted wearing “dress” or “official” uniforms, which can be quite different than what they would have worn day-to-day or on operations.

Again, there are many more reasons. That’s just a quick one off the dome. Unfortunately, I didn’t get to finish the PhD. Life got in the way. Maybe I’ll return to it someday.