When did this happen? For item ID support client side to increase from 65K to up in the billions the ID's had to have changed from Short to Int value which means new packets. What are the packets?
in packets item id field size increased from int16 to int32 from 2018-07-04 RE
about valid item id i not checked. probably it still limited to 32k or 64k.
Also interesting fact. in player move/stand packets increased only weapon field and not other slots. probably this mean big id will be used only for non equipment?