this is a very serious matter. In the 12,000 man host at winterfell bolton has 3500 men, karstark 2300, manderly 1500. umber, hornwood, cerwyn, flint, ryswell, dustin altogether should've brought at least 4000 men with them. If glover and talhart brought 700 men, which is ridiculous, then the levy of house stark would be 1200 men( added to 600 at winterfell).
Of the remaining 6000 most 1700 come from manderly and the rest from the neck.
Even if we consider that 1500 out of Ser Rodrik's 2000 men where stark men then that still gives winterfell only 2700 swords!!!
House stark held the north for 8000 years, when there where no karstark, manderly's. They controlled such a harsh people, crushed repeated rebellions, kings beyond the wall and skagosi. And earned the fear and awe of their bannermen. I strongly doubt they did this with only 3000 men.
And looking at the north. The karhold lands are deeply wooded and smaller than the wolfswood and they field 2300 men. The wolfswood being twice as large and being under the starks for some time( glover is master under winterfell) should give at least 3000 men.
And furthermore the main winterfell land is characterized by a triangle like river in the south and mountains in the north. This is a plain land and much bigger than the bolton lands and it is surrounded by rivers meaning fertile plains. This land too should yield more troops than the boltons, at least 4000.
Then there are the talharts who also are masters and look out for a large plain land.
They too must have a 1000 men.
So, a tally of 8000 stark men is much reasonable.
So i'm not sure whether this is a writing flaw on part of george martin or if this is deliberate to stage the makings of a new Stannis/rickon host.