It's pretty much a game of musical carriages; the following 455s are not in their original formations:
455 801 - contains one driving trailer from 455 825 and the trailer from 455 821
455 802 - contains the trailer from 455 828
455 808 - contains one driving trailer from 455 830
455 809 - contains one driving trailer from 455 823 and one from 455 812, plus the trailer from 455 812
455 812 - contains one driving trailer from 455 809 and one from 455 824, plus the trailer from 455 809
455 816 - contains one driving trailer from 455 828
455 818 - contains one driving trailer from 455 827
455 819 - contains the trailer from 455 801
455 821 - contains the trailer from 455 819
455 823 - contains one driving trailer from 455 812 and one from 455 809
455 824 - contains one driving trailer from 455 808 and one from 455 823
455 825 - contains one driving trailer from 455 801
455 826 - the driving trailers have swapped ends
455 827 - contains one driving trailer from 455 816 and one from 455 818.
455 828 - contains one driving trailer from 455 827 and the trailer from 455 802
455 830 - contains one driving trailer from 455 824 and the motor from 455 835
455 835 - contains the motor from 455 830
Note that 455 816 has two odd numbered and 455 827 has two even numbered driving trailers.
Some units, you will see, have swapped three carriages - they retain the unit numbers they do because convention on the Southern area is that it is the motor vehicle which gives the unit an identity - so I am rather puzzled why 455 830 and 455 835 swapped motors without swapping their identities.