The EBII team did a good job of maximizing the chances that the armor upgrades occur in chronological order.
1. Thorakitai reforms
2. Barcid reforms
3. Barcid panoply reforms
4. Marian reforms
5. Celtic twilight reforms
However, it's still possible for a later reform to occur first, activating all prior reforms. In my Makedon campaign my Katakoi Thraikes suddenly obtained their armor upgrade despite the Thorakitai Reforms having not yet occurred. Turns out AI Carthage conquered Gadir and turn 140 has passed, thus triggering the Barcid reforms and by extension the 1st and 2nd armor upgrades. This post isn't really a criticism of the system - EBII's armor upgrade system still accounts for the limitations of the M2TW engine. However, it does allow for some odd events, such as the political reform of Carthage's government causing Thracian Colonists to acquire more armor.