Yes, I am sure they do. It is also why the books have such a huge advanatge over players right now. With so many books and so many laying off or betting with each other, they can hold lines at "unfair" rates or numbers much longer.
Even the big boys. How hard is it to think that if they are buried, and I mean buried one way, they might not call a few mid level shops and ask them what theri balance sheet says. If the small book is not so heavy then the big book might say, "Well if you take this amount off us then we can hold this line alittle longer, and protect us and you too" The big book does that with 7 or 10 smaller books and they can hold a line indefinately.
Let's face it, three to five books pretty much set the market line for the whole betting world. So if they can lay off and balance action amongst themselves and a group of other books then they can hold lines and odds alot more. Probably do not do it all the time, or in spots that are not necessary.But do you think right ow with so much money one way on New England that they are not doing it somewhat? Do you think ANY books wants to go to 7.5? Everyone and their brother would take the buy back, opening every book up to potential massive losses.
It happens, that is why trying to find value these days is nearly impossible.