All armour variants are canon. I don't know where you get this impression.
However, you seem to have a different impression of how they operate.
The MKIV, MKV, MKVI and GEN2 are different platforms with optional upgrades (IE EVA, EOD and so forth) in the form of armour plates and specialised technology.
It's Kurt (SPI), Kelly (MKV) and likely Will or Linda (MKVI)
Thanks. So you're telling me that all the variants are additions to the Mark VI armour sets? E.g. The EVA seen in Halo 3 is another version of Mark VI, developed after Mark VI was first deployed?
I assume Linda/Will had Mark-VI because they were redeployed to Earth after OPERATION: FIRST STRIKE, am I right?
As previously asked, why did Chief remain suited in the standard Mark VI armour? Even other Spartan-IIs were given a specific variant of the MJOLNIR Mark VI [GEN2] to suit their specialty. The Mark VI in its original form seems to suit no purpose, and almost comes off as inferior to other armour variants because it doesn't excel in any specific area. Why was John left with the standard Mark VI [GEN2]?