If the project is 2.1.27 it should be exported with 2.1.27, not the latest editor version, and you should use runtimes that are compatible with data exported from 2.1.27. Looking at the releases, the runtimes were tagged with 2.1.25 on Mar 29, 2015. Looking at the cocos2d-x runtime commits (I'm assuming, since you only said "cocos2d" for what runtime you are using), it looks like commit 371aaefa9fc8cb041d59f727ad9e7f2ad31cd405 would be a good choice, as it is after 2.1.25 but before any new features (additional blend modes) were added to the cocos2d-x runtimes. You can download that commit here.
Using 2.1.27 is fine if you don't need editor or runtime features after 2.1.27. Otherwise the animator could update the project to work with the latest editor version, then you can use the latest runtimes.
Runtimes aren't tagged with an editor version more frequently because we only make a tag when ALL the runtimes are updated to a specific version. As runtimes are updated, new features are added and others become out of date. Recently we started a new system where each runtime's README specifies what versions it is compatible with (for example). This allows for better tracking down a particular runtime for a specific editor version.
