SIA ordered the A343 in 1991/2. They had an add-on order in 1994. Even in 1991/2, Boeing was offering the IGW. SIA didn't consider the B777 in 1991/2. In 1994, SIA was close to considering the B777, but only as a supplement to the A343, but SIA stuck with the A343.
In 1995, Airbus was struggling with meeting the SIA's specs on the A343, SIA wasn't pleased with Airbus' progress, and Airbus had to delay the delivery of the aircraft to March of 1996 instead of the contract date of late 1995. At the time, they were requesting the two manufacturers to make their bids for replacing the A312/3s. Originally, the order was for 17 firm plus 17 options. Because of the A343 performance problems, SIA more than doubled the orginal requirement and asked the two manufacturers to make fresh bids. In November, Boeing won the 34+43 B777 order. The future fate of the A343 was long penciled in with the B777 order, but SIA only officially announced it in 2000.