A few days ago had a flight GRU-IGU with Light fare. Purhased the tickets directly from LATAM website. During the booking process added BA ffp number(G) and after finishing the purchase a ticket printout showed 23kg permitted. A few kilos more did not make any issue in counter check-in.
When I redeem EY miles for G3 flights the fare has been always luggage included,despite a Light fare availability. Just for the note.