I have been searching for eons to find out exactly what is a "LIGHT SWAP ENGINE" and what a region "swpp" firmware exactly means. No idea really.
I have observed that usually they have lower version numbers and never get updated.
Two theories:
1. they might work as an intermediate "downgrade" step when swapping to a different firmware.
2. perhaps it is the default firmware for a replacement board and can be flashed to anything.