Can grafts get damaged even after you don't see blood after combing?

Anything is possible and the abssence of blood is not an idicator.However, after 15 days the grafts should be secure.

Definetely the grafts might be damaged without any sign of bleeding but for your case most probably there is no such problem.In my practice I always advice my patients to have their hair cut with scissor which is less risky then trimmers.Combing and daily washing without scratching should not cause any problem after 15 days.

I would advise you to always review the scenario with your hair transplant surgeon as well.Grafts can certainly be injured even if you don't see blood. This first 10 days are by far the most important. After15 days the grafts are at minimal risk from damage.  You can be fairly vigorous with washing at this time point without much concern. Combing and scratching are very, very unlikely to cause permanent damage at day 15, unless of course it's extreme.

After this long it is hard to really do any damage to a hair transplant. If any damage occurs its usually in the first week. 

At 15 days after a hair transplant, the grafts are pretty well seated and are difficult to remove under normal circumstances.  There was an interesting study performed which showed that by 9 days after a hair transplant, the grafts are difficult to remove.  I recommend to my patients to be very careful for 2 weeks following surgery, then they don't have to be worried that a graft will become dislodged.  

I have found that unless your stylist understands the care of a hair transplant and uses ultra clean combs (often many do not), you are a set-up for an infection. If you want a hair cut, that is ok, but make sure the person doing it knows what you had and how to handle your hair and scalp.

Usually after 7-8 days you can start to play with the scabs so they fall off. You do not want to forcefully as you may get some follicles along with the scabs. You need to still be gentle for up to two weeks.  However, after two weeks the grafts are settled and the chances of follicles coming out is very low.  Usually when our clients come in for a two week follow up we clean all the scabs for them, there is no need for concern at this point.