Quantitative review contain question which is not in official guide. Questions of various difficulties are distributed uniformly. So may be you solved the questions form less difficulty level or you aptitude is now at that level where you can solve higher level questions easily.

In my opinion the difficulty level of the quant questions in the Official Guide 13th Edition and Official Guide Quant Review 2nd Edition is about the same.

The only difference is that the OG 13th Edition has more of the recently retired GMAT questions, although as a percent they are still a small fraction. Many of these recently retired GMAT questions are fairly difficult and are distributed somewhat randomly in OG13 and don't really follow the supposedly increasing difficulty of the questions in the Official Guide. I believe this is mostly because GMAC is lazy in properly ordering the questions by their correct difficulty level.

Here are some examples in the Official Guide 13th that don't follow the difficulty trend:
Problem Solving: 56, 64, 66, 71, 77, 80, 95, 111, 112, etc.

Obviously I can't claim that the above questions are definitely harder than the rest in that category, because I don't have access to the statistics on these questions. However, I am pretty certain that they are harder on average than where they are placed in the Official Guide.

All of these problems are retired GMAT problems from over the last five or six years since Pearson took over writing the GMAT.

Cheers,
Dabral

Agreed, the difficulties are comparable... Also, I think that for the most part the increasing difficulty theory is correct, but there are a few outliers. Often learning the correct approach to the GMAT can illustrate how some seemingly difficult questions are actually pretty easy.