Are they really doing 5, 6 and 7?
Remember the powers-that-be at CBS wanted all seven seasons out in three years (2012, 2013, 2014). So that meant CBS-D needed a little help with at least a couple of seasons. CBS-D is about to prove that they can do two seasons a year (S3 and S5 will be done by them for release in 2013). It's that request for three seasons in 2013 that really seemed to make a need for some extra help.
So when you figure the remastering work on Season 4 is all but done now thanks to Modern Video's help, CBS-D has surely already moved on to Season 5, and then when that's done they have the luxury of doing only two more seasons throughout the entire year of 2014. So for example if the higher-ups allowed it, Season 6 could be mid-2014 (instead of early 2014) and Season 7 could be end of 2014 to give them lots of time.