You will probably get may 2013 126.96.36.199.18 (RDBMS) on 188.8.131.52.1 (ESS).
You can find some details in 888828.1 (or follow link https://updates.oracle.com/Orion/Services/download?type=readme&aru=16223374) to find what has been fixed.
Yep - got the May 21 build (BP 18) and it arrived four days later (that's what you get for ordering at Oracle's financial year end!)
I've checked and I can't find any difference in functionality in the documentation that you referenced. I'm not surprised given that Oracle seem to save functionality changes for Release levels and have the Patchset levels fix bugs.
Thanks for the link