The CE's in 2 different locations are using the SAME BGP AS number (AS 100) so inherently they won't exchange routes due to the loop prevention mech. That being said, using AS-OVERIDE on the neighboring CEs will replace any AS number (AS 100) that is the same with the PE AS number (AS 1), thus allowing connectivity.
The purpose of BGP SOO, which is a BGP extended community attribute, is to provide a loop prevention mechanism. A route-map applied on the PE to 2 CE neighbors "tags" the prefixes learned with a SOO. When tagging to 2 CEs off the same PE, the effect is that the PE won't advertise a learned route with the same SOO to another CE, effectively preventing a loop. An assumption is that the 2 CE's have a backdoor connection between themselves.
1 Thing to note, the solution guide config for SW1 doesn't have a bgp neigh peer statement for SW2, iBGP. But SW2 has a neighbor statement for SW1. (since one side is missing they are not iBGP peering)
On to the next one.
