Studios used only to record orchestration are not listed, nor are additional studios used for mixing and other work. The lead vocal refers to soloists and the leaders of group vocals. Some Bee Gees songs have more than one lead by this definition. Some blended vocals may be misidentified and I'm open to discussion on these. Barry and Robin sing most Bee Gees leads, but despite the impression that may be given, Maurice sings on almost all Bee Gees songs, as harmony or backing vocal.
Time is the longest time known, where there is any variation.
The most common variation is in fadeouts, which may be cut slightly short on some records where the song appears. Times for unreleased recordings, when given at all, are approximate, subject to speed problems with unofficial tape copies and to lack of an authoritative source for fadeouts. The mix is identified as mono or stereo and sometimes with additional wording. We have no documentation on any mixes, except the edits identified by name starting in the late 1980's, so I have identified separate mixes prior to that time solely from listening. The format is usually any of single, LP, CD, and unreleased.