I would rephrase that to: The term tier can apply to different concepts and can have a different meaning in each case. The loot is tiered and weapons and tools are tiered, but the tiers have nothing to do with each other.....
To get all detailed about it, there are 3 tiers to melee, hence why people use the term "T1, T2, and T3", but with the primitive age added, they can now be reclassified as T0, T1, and T2. Basically, the term "tier" now has 2 different meanings: the age in which it is crafted/looted, and the number of melee weapons within the class itself. In other words, there are two definitions to "tier": the age in which that progression level of melee is found (so Tiers 0-3), or it could simply mean someone cataloging that there are 3 levels of progression through melee. So, tiers 1-3, which now have nothing to do with the age in which they are found.
Make sense?
The independance of the two tiered categories is evident when you look at primitive and iron weapons who can be found in higher loot tiers as well.