In the 2001 ncees there are couple problems that seemed a bit difficult than whats on the 2016 and 2011. In the 2016 most values are given, in the 2001 you have to go backwards at some problems like SlayPE problems.
But it is still straight forward questions, just "more work" to do, but if you have good understanding of the process you should be good nothing to worry. Take it as just longer to solve problems but not necessarily hard.
And side note, I spend more hours in 2001 ncees than the newer ncees.