CECH20** models were released in September 2009 and use the DYN-001 motherboard.
CECH21** models were not released until March 2010 and use the SUR-001 motherboard.
You should be looking at the PS3devwiki. This will tell you all you need to know about PS3's and has way more info about them than that wiki your looking at.
https://www.psdevwiki.com/ps3/
Also the first 2 number's in the model have nothing to do with region they were for, thats the last 2 numbers eg CECH20
03A is a UK 120gb 1st gen slim. I have 2 of these PS3's.
CECH = whether is its retail or debug [DECH is debug]
20** = model
**03 = region [ 00 = Japan, 01 = USA, 15 = Canada, 03 = UK,
A/B/C = model variant, normally what size HDD it comes with stock.
This is for Slims and SuperSlims. For Phats is was slightly different.