How to log extentions

I was wondering how you log a climb with an extension, specially when the grades are close and by on-sighting the first part, then red-pointing the extension. Would it be correct to log both climbs (e.g. climbName 7b+ onsight / climbName+ext 7c redpoint), or should you just log the extention as redpoint (but in this case you'll get less point than just log the first part onsight..)