I think it's a historial thing. Most of the other caravan mags are just as far ahead of themselves.
My guess is that at some stage in the past one mag brought its issue next forward a few days to get on the newstands before its rivals. In turn the rivals brought theirs forward, and so on and so on, each wanting to be fist on sale.
They've obviously stopped that race now, but are left out of sync. If they'd only kept going they would eventually have caught up with themselves - a year ahead.