Hi
AmanKidCACSIt is great to know that you have a great target score & you're striving hard for it. Additionally, I quite agree that GMAT Prep are the closest indicator of what you might end scoring on the GMAT. Having said that, I'd like to tell you that it is quite subjective to mark a comment on questions such as "I have a current GMAT Prep score of V 25, can I take it to V 40?" or " I have observed a lot of inconsistency lately in different mocks in my Verbal score. What and how to do?" or "Is it possible to increase your GMAT score by 60 points in 3-4 weeks?"
I would say if you think you can, then you can. Identifying and working on what went wrong will definitely work for anyone and everyone. I am NOT against any prep company when I say that they are here to offer you the right resources and direction! My point is ultimately it is "you" who'll have to earn that score. If a prep company guarantees a 60 point improvement and you are not genuinely studying hard for it, nothing can help!
In short, to answer your question - Yes, it is possible to improve from V 35 to V 43 if taken the right steps.