Do you mean OS version as in 4.2.0.21 rather than 4.1.0.24, as images certainly are different? However if you are comparing hybrid-recovery.img 14.3MB from F5121 and F5122 versions (4.2.0.21), without checking every single line of code they do appear remarkably similar if not identical. Don't know whether anyone in a position to confirm or deny this.