it has been like that for ages, Borella is correct.
t3:
lvl41 white belts (obsidian fortress, do you remember?

)
t4:
lvl48 purple - t4 (Bosburs/Shrine of Pasper)
lvl54 blue (SL Nagas)
lvl58 green North Janost Forest (for sure, dont know if we had 58 green drops in SJF)
lvl61 white => belts in limo desert from vendor.
only orange items behave a bit strange, Annelia level65 orange items are t5 already, and back in the days the level50 orange stuff from Binpikes and Ant Queen jumped a tier.
See the pattern? It really has been like this for 2+ years unchanged.