Problem Supporting Old Rokus

Hi all, I've encountered some documentation discrepancies that make it difficult for me to support old firmware. Specifically, the documentation indicates that roMessageDialog.addLeftButton was introduced in firmware version 2.7 (http://sdkdocs.roku.com/display/sdkdoc/ifMessageDialog#ifMessageDialog-AddLeftButtonidasIntegertitleasStringasBoolean), however I attempted to use this method on a roku running version 3.0 and it failed.

Are there any documents which are more up-to-date that I can use as a reference for when methods were added?