Thanks Aashray. Yes, I can get the api version using system-get-ontapi-version, but developer should know what APIs are compatible with version of OS. That's why it is good to have matrix in place.I know API guide has what is new and changed, but don't have versions.Developer can figure out by going through all versions if required, but we can't expect that everyone has all OS installs or docs in hand.
Anyway for me it was easy that APIs are new in 1.20, so i can check 1.20 onwards while developing an application. It would always not be a case.