Artist Members can extend unlimited full-track Promotional Previews on releases with no play limit to other co-op members. This is enabled in upload settings, based on a Direct License granted by the uploading artist to other fellow co-op members.
Artists can choose to opt out of this setting for any of their releases, in which case the standard 3-play limit applies to everyone. If you're a member and finding a play limit on a particular release, the artist has likely disabled unlimited member previews for that release.