user: Question: What is the latest year of a Gratitude type mission with 99 in the entourage?
Columns: ['Year', 'Mission type', 'Shogun', 'Ryūkyūan King', 'Lead Envoy', 'Number in entourage']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1634.0, 'Congratulation & Gratitude', 'Tokugawa Iemitsu', 'Shō Hō', 'Princes Tamagusuku, Kin, Sashiki', 'Unknown']
SQL:

assistant: SELECT MAX("Year") FROM "Table" WHERE "Number in entourage" = '99' AND "Mission type" = 'Gratitude';