As we all know, IATA makes controlled duplicate assignments of airline codes, usually to (secondary) airlines in different regions of the world that are very unlikely to overlap their route maps.
Also airline codes get re-assigned after so-and-so many years of inactivity.
Have you flown on both airlines having the same IATA airline code ?
This either may be codes issued as controlled duplicate or assigned to different airlines of course of years.
My humble contribution is. BX
Back in the 1970's flown while being assigned to Spantax of Spain (ICAO: BXS)
Currently assigned to Air Busan in South Korea (ICAO: ABL) and used in 2011.
P.S. BX also was assigned to Coast Air of Norway (ICAO: CST), but also this airline is defunct since 2008. During the years of 2007 and 2008 BX was a controlled duplicate of Coast Air and Air Busan..