Lines 17-20 make it possible that the ORIGINAL owner has 100% of the rights, that the NEW owner has 100%, and everything in between.
So I'm not sure what contingency you're worried about.
You're saying we have no proof that any right has ever ACTUALLY been transferred, only proof that it's POSSIBLE to transfer 1-100% of the rights?
A few things there:
1. Don't be crazy.

I say this with LSAT parental love. You're not going to do as well on this test as you could if you're worried about exotic logical loopholes like this. Lines 17-20 are absolutely conveying the commonsense expectation that SOMETIMES all the rights are kept, SOMETIMES all the rights are transferred, and SOMETIMES it's in between.
2. The question doesn't ask for PROOF, it asks for MOST STRONGLY SUPPORTS. You can't demand 100% proof from that question stem. The right answer is the BEST supported, not necessarily perfectly supported.
3. Finally, and not to undermine the previous two points which are more broadly helpful to LSAT studying, (C) doesn't say that SOMETIMES people transfer the right to profit. It only says that it's POSSIBLE.
"compatible with" has the same meaning as "consistent with" on LSAT. They are super weak-sauce. They mean "non-contradictory".
"All mustard is yellow" is compatible with "The Redskins should change their name".
Those two statements do not contradict, thus they are compatible/consistent.
"All mustard is yellow" is incompatible with "All mustard is red".
== other answers ==
Given the open-ended nature of this question stem, the most important thing to read for on a first-pass is "danger words", stuff that's too strong, too precise, or making a comparison we never made.
(A) "most" transactions involving non-intellectual property ... did the passage tell us what's true about 51% or more of transactions involving non-intellectual property?
(B) "only" those areas of law ... nothing is that restrictive
(C) correct answer (it doesn't get any more weakly worded than "compatible with")
(D) "sufficiently protected" ... we can't find anything like that, and the author's misgivings in the final paragraph sound more like the opposite of this.
(E) "only if" is too harsh ... nothing is that restrictive