Yes, there is a record of command upgrades and this policy has just been revised and published.
There is a strong probability that an FO will be offered the opportunity to upgrade in the first 5 years, realistically after 3 to 4 years of joining.
Look carefully at the requirements to join as an FO, the salary being paid. Pretty crappy deal if you're not living in the US, considering the performance of the US$.
Also, AJX has been experiencing a very high failure rate of new hires, possibly as high as 50%. The failure rate applies to both new hire capt and FO. The sucess rate of upgrades so far is very good.