OK, it seems like you're very confused. Please do the following -
- Take out your PSP's battery and and UMD in the drive.
- Put the battery back in.
- Turn on your PSP.
- Go to Settings - System Settings - System Information.
If 3.03 OE-A is listed here, then you've flashed your PSP to 3.03 OE-A and all traces of 1.51 have been wiped from your system. 1.51 is gone, it is no longer your firmware. Your PSP doesn't know it was ever 1.51. You can just forget that 1.51 was on your system; it makes no difference now. 1.51 has been completely replaced by 3.03 OE-A.
What I'd do now, if I were you, is upgrade to 3.80 M33. This takes a while, but it brings great benefits. To get to 3.80 M33, you first need to upgrade from 3.03 OE-A to 3.52 M33, then to 3.52 M33-4, then finally to 3.80 M33, with an optional upgrade to 3.80 M33-2..