Is there a requirment to get level 19 uncut gems to start dropping?

I'm 89, doing T15/16 maps with corruption/irradiated and I haven't found a single level 19, all I get are 17s and 18s. My friend is doing the exact same content and finding loads so I have no idea what's going on.

Think you need to be lucky enough for them to drop from rares (+1 to ilvl) and bosses (+2 to ilvl)

The only ones i´ve seen dropped when we were partying as three people.

Might be the same calculation as Inc.Item.Rarity where we have to roll a dice in T15maps to roll that "Tier" of gem over to lvl19.

You could skip that step and go directly bosskilling at lvl20 gems.

I generally only find them at drop levels of at least 81.