data sufficiency

Certainly it is possible that on a yes/no question the statement (or statements together) could give you an answer of "always no." I would say that it may seem that there are more instances of getting a "yes" and this may even be true.

Here is the one simple thing to do for yes/ no data sufficiency questions: Instead of "sufficient" use the word "consistent." Does that statement give me a "consistent" answer. Consistent could mean that you get a "no" for each possible value, of course it could also mean that you get a "yes" each time. So the answer to your question is, certainly it is possible to get a "no" and to be sufficient.

Here are a couple of data sufficiency articles that I have written that might help you out:
https://www.beatthegmat.com/mba/2012/10/ ... -handrails

https://www.beatthegmat.com/mba/2012/01/ ... ufficiency

Brent has stated it exactly!

People get confused as to what "sufficient" means.

If the question is "Is x > 9?" many people believe that in order for a statement to be sufficient it needs to show that x is greater than 9. So if they find that statement 1 indicates that x = 8, they will say that this is not sufficient. Of course it is sufficient because it is "consistent." 8 is less than 9 so the answer is a consistent "no." Even if there were several values x = 8, 3 and - 12, all three of these values are less than 9 so this would be "consistent" and so it is sufficient.