BOLTON — When training camp begins Friday, it might not be the first time this current Celtics crew will have worked together. Unbeknownst to the coaches, the veterans gathered the core members of the 2012-13 team for workouts last week in Los Angeles.

Several rookies and free agents joined Kevin Garnett, Rajon Rondo, and Paul Pierce at UCLA for informal practices, perhaps a sign of the vets’ seriousness in approaching this critical season.