Square?
I don't think any airline, can show you a contract with a guaranteed time to upgrade/transition (I do know Sichuan airlines offer 330 transition after 3000hrs on 320 in their contract, but with stipulations). There are so many variables in that equation, from Individual performance, airlines performance and continued expansion, political emphasis on localization of cockpit crew, feedback from simulator/Insructors/Crew Rostering, your ability to afford the upgrade etc..
As I mentioned to Mig54, they do offer upgrades; transitions apart from a couple that left the 320 & came back on the 330, not so much, after taking 10 guys from the 320 maybe 4yrs ago(?) maybe only 2 expats has transitioned since. Some are hoping that the arrival of 350/787 will change that, but your probably going to need deep pockets, for that privilege..
ATR not sure of the numbers but don't think so many in last 3 years.
Mostly upgrades for 320/330 expat FOs to LHS 320.
So agencies are not lying if they say it is possible, it is...but?
Square- you can't blame the agencies for sugar coating things a bit, their business model is to make commission off of the backs of the contract pilots, not to scare us away.. It is up to each pilot to do there own due diligence..
That they have a bit of a retention problem, despite the cheap beer and friendly women, regardless of what is said good or bad on this forum, should help in the due diligence.