Maybe they're restricted on the announcement until another festival sells out of tickets (EOTR / Latitude etc.)
Which is why they can't be more specific about the actual date they can release the final lineup.
Here is a link to the Chai Wallahs 2019 festival line-up poster, which should include the Green Man acts:
(Some bands will only be playing Kendal Calling or Shambala) https://www.chaiwallahs.co.uk/festivals-2019/
Although reading the article on NME it states:
“It’s great to be doing the Saturday night Mountain Stage slot at Green Man 2019!” said Four Tet.
After claiming they are headlining Friday........So who knows ?
Great journalism there.
Four Tet are Headlining Friday:
Eels are confirmed for Sunday: