I mean, technically you don't even have to make a mark in the test booklet. But yeah, you can do that if you want but like Alex said, you might risk getting confused at some point.
@"Alex Divine" That's actually the reason I upgraded to Ultimate+, to get access to the LR from the earlier tests. The explanations for LR are from PT's 17 onwards, and RC explanations are from PT's 1 onwards.