I've just unpacked a new G-Shock from its tin, and first checked the time. It was 24+/- 2 seconds ahead. Production date was 2012-12-19.
From the looks of it, it has not been touched at the dealer. No fingerprints, no slightly damaged edges in the booklets. So i suppose it has not been removed from its tin since it was produced, and therefore was also not able to synchronize with a time signal since.
(It's a multiband 6 watch/GW-A1000). Half a minute in about 16 months would be an inaccuracy of around 2 s a month.