Before year 2000 there were only 3-4 type of notes were in market.
In year 2000 there were only few say less ten type of notes was available for iit jee exams. But after the rise of Kota coachings and other city iit jee coaching classes almost every institute claimed to have best iit jee preparation notes.
Most iit jee notes were prepapred by faculties of iit jee coaching classes and it was an extra work for teachers beside class room teachings.
Most notes were made from various Indian and foreigen auther books. And problems either were taken from books or past papers from various exams or framed by teachers.
It is found that many problems are from international books and problems framed by teachers are errorful and many answers were not correct.
The problem asked in iit jee past paper was only perfect problems.
All coaching classes claims to have high level problems which is usually framed by teacher, and such high level problems are part of a race to claim to have better iit jee preparation notes than others.
This race makes many lakhs of students fool every year and actual use of such problems has nothing. In Kota every year more than 50,000 students solve such high level iit jee problems and they could not solve many simple problems in iit jee exam.
So as for as level of problem is concerned all is not well. And most of coaching notes contain out of iit jee syllabus theory and student thinks
it is of high level which is a deal of wastage of time and money and nothing else.
Best is to read all syllabus carefully and then select books and study notes.
And it is best to make own notes for formulae etc. and refer standard books only.
Even if You still need such notes search internet tons of notes from Kota are available for free.
Auther iitjee master