The most likely reason for the decreases in your verbal score is that the tests you took after the first one are not quite the same as the first one and, therefore, have generated scores lower than the score the first one generated. Since, the GMAT Prep test is, of the tests you took, likely the most accurate representation of the actual GMAT, the score you got in verbal on that one, V41, may be your current verbal skill level.
That said, your V41 score may have been a fluke. Alternatively, it could be that, since you took that official practice test, you have changed your approach to verbal in some way that has resulted in scores lower than the one you achieved on that test.
Finally, it could be that there are holes in your verbal knowledge or strategies such that, when you see certain questions, you score relatively high in verbal, and when you see questions that reveal the holes in your knowledge or strategies, you score a bit lower.
Of course, one simple way to figure out what's going on is to take another official test if you have any left.
Regarding how to drive your verbal score higher, generally, untimed analysis of every answer choice of many verbal questions is the surest way to develop an eye for what you need to see in order to answer verbal questions correctly.
_________________
Marty Murray | Chief Curriculum and Content Architect
See why Target Test Prep is the top rated GMAT course on GMAT Club.
Read Our Reviews