Nice question, but just one small problem:

"In prefix compression, does the entire prefix stored in the header need to match the data to be used?"

--> requires the answer NO to be correct

"In other words, if I have a prefix of "aaabcd" in the header and a data element of "aaabfgr" in a field, can prefix compression be applied?"

--> requires the answer YES to be correct

I chose NO, but apparently that was the wrong one, although I meant to answer the first question.