Proposal:Member Of Band Relationship Type modification

If the person artist is still a member of the group artist, leave blank.
If the group artist has itself has ended, and the person artist was a member at that time, use the date that the group artist ended.

There is no guideline yet for how this attribute might be used.

This attribute indicates that the person artist was a founding member of the group artist.

Guidelines

Some person artists leave a group artist, then rejoin again later. This should be represented through the use of more than one relationship between the person and group artists, with the appropriate start and end dates set.
If a person artist is usually known by a particular performance name, use that performance name to link them to the group artist instead of their legal name. If the artist uses multiple performance names, the performance name that should be used is the one that they usually performed under whilst in the group artist.
The conductor or chorus master of a group is almost never also a member of that same group. The Member of Band relationship should only ever be used to link a conductor or chorus master to the conducted group if that person is credited as a member of the group; it should never be assumed without such evidence.
Rationale
Artists are usually credited by their performance names, rather than their legal names. In fact, the real names of some very well known members of group artists are quite obscure. If an artist's legal name were used to link them to the group artist, instead of their performance name, this would create confusion, and likely people would try to link the performance name anyway.

See Founding Member Dates Question for the original discussions which took place regarding how to handle founders.