Oracle has introduced the concept of "Codelevels" and "Codelines" in the new E-Business Suite Release 12. The first base release in R12 is 12.0 (also called Point Release). All the patches introduced on top of this point release are said to be on Codeline A. 12.0 is also called the Codelevel A. The next Codelevel in R12 is Codelevel 12.1 and its Codeline is B. Similary 12.2 and Codeline C. Compare this with the E-Business Suite 11i version when Codelevels were instead called as maintenance packs (11.5.8, 11.5.9, 11.5.10 etc.) Furthermore, Oracle says in one of its support notes, that it is "not possible to apply a Codeline A patch on an E-Business Suite system that is already on Codeline B (12.1 point release)". So that should mean that Codeline A patches are not compatible to apply on a Codeline B system.
Our E-Business Suite system is on 12.1 point release. The other day I was analyzing a patch xxyyzz.R12.AR.B to be applied for fixing an "Accounts Recievables" issue and I noticed a few discrepancies in the patch's README file.
Issue #1 (Prereqs)
The README mentioned several prerequisite patches to be applied to be applied prior to applying the actual patch. One of the prereqs mentioned as a Codeline A patch aabbcc.R12.AR.A. I checked with the Oracle Support team and they mentioned that its a "typo" in the README and it was immediately taken care of.
Issue #2 (Postreqs)
The README mentioned several postrequisite patches as well and one of them was a Codeline C patch ! ppqqrr.R12.AR.C. This time the answer from Oracle Support was not an expected one. As per Oracle Support, some of the products on 12.1 release have been using the C codelevel due to an intermediate release of some vertical products falling in the same product line. So in 12.1, one can see some products with the C label too.
Please seek a clarification from Oracle Support (in the form of a Service Request) if you find a patch that contains prereqs and postreqs from different Codelines. Most of the times it could be a typo in the patch README and sometimes it may be a valid case !!!