Hi Hava,
There are two parts to my answer:
GDB Version Support:
CDT has a very wide GDB version acceptance. Current CDT works with all versions of GDB since approximately GDB 6.6 through to the most recent GDB releases. However we test and fix against a slightly more limited version range of GDB. Since CDT 10.3 we support/test against GDB 8.0 and newer. Older versions of GDB should still work, and patches will be accepted against them, but no active effort is in place to make such old versions work.
As a reference, GDB 8 is approximately 5 years old already.
If you need information about what was tested in older CDT releases, see dsf-gdb/org.eclipse.cdt.tests.dsf.gdb/src/org/eclipse/cdt/tests/dsf/gdb/tests/ITestConstants.java
Naming of files in DSF-GDB
The version numbers in the DSF-GDB files refer to the minimum version of GDB. For example GDB 6.8 will use GDBProcesses, GDB 7.4 - 7.9 will use GDBProcesses_7_4 and all versions since GDB 7.12 will use GDBProcesses_7_12. GdbDebugServicesFactory is the class in charge of converting the GDB version to the appropriate version of the service.
Please ask follow up questions if there is anything unclear, and please let me know if that resolved your question/issue.
I hope that helps,
Jonah