BR gives him a team-best defensive rating this year, and last year he was one of the team's best.
We've already been over this. BR individual defensive ratings are completely worthless.
Which defensive measures are worthwhile?
Just about anything that isn't calculated as a bizarre combination of steals, blocks, defensive rebounds and opposing team shooting percentage. Which is roughly how they do DRs over at BR.
I prefer opposing player PER as a rough measure with all the caveats attached. I'm sure stats.nba.com has better stuff, but I can't navigate that site for the life of me. I guess I'm old?
Also, 82games updates rarely, but does have a notification about the time of their last update:
Boston Celtics
2014-2015 NBA Season Stats
Last update: 2/18/2015