YMMV
Last year I booked at SIN-LHR-Canada trip with BA Singapore in WT+
Alas not early enough to get the T class fares.....
But my Perth TA was able to pick up the reservation. And because of the the increasing value of the AU$, was able to help me avoid the currency exchange charges as well as save a bit on the base fare. And she was apparently quite happy to pick up a premium fare ticket.
From there it got even more interesting. The AA fares I needed in the US/Canada were checked on aa.com. The TA checked booking the flights through BA (in conjunction with the long haul). A set of fares that were actually a fair bit less expensive
. Yes I lost the 1000 miles or so I would have got for booking the 6 segments on the website.... And yes the sticker upgrades worked on ALL the segments, including the one at the airport after thunderstorm disruptions at DFW.
Will it work for all scenarios?..... read the first line again
Oh yes EZE. You might want to check the cost of SIN-SYD-SCL and SIN-SYD-EZE - assuming you can talk with a TA. The savings might be substantial if the fare class seats are available.......
Given that SIN-PER-SIN is roughly the same price as PER-SYD-PER it would be a non-decision for me.....
Happily wandering
Fred