Some dont have duplicates some may duplicate twice, i know moda doesnt duplicate but i havent used other brands

I'm working on creating my own layer cakes and jelly rolls - I have so much fabric and this is a good way to use up pieces!

I've gone through a number of Moda layer cakes, and in general I see a handful of duplicates in each pack. Once in a while on a smaller line there will be a triplet or two. When I am cutting my own layer cakes (for specific patterns) I try to make sure I have a good balance of light v. dark pieces (50/50 if I can get it), and an eye-pleasing mix of strong designs and colors v. solids, blenders, and more "restive" pieces.

Moda DOES duplicate in some of their charm packs and layer cakes.

I just used 4 Moda charm packs to make a quilt and there were no 2 alike in color but there was 4 different colorways.

I think it depends on how many fabrics are in a collection and how many color ways. The Ruby charm packs have the same prints but in different color ways and there is a pin dot fabric in each color way that there is 2 charms of each. Moda is consistent in keeping the count of their charm packs at 40-42.

I've used many Moda layer cakes and charm squares, I have rarely had duplicate squares. As mentioned, it depends on how many fabrics are in the line.

I have yet to use a charm and/or layer cake that didn't have the pattern duplicated in different colors.

The early Moda charm packs had varying totals of squares, from 30 to 40 or so, but they all seem to have 42 now. Layer cakes are 40-42. Duplicate prints depend on the fabric line, some lines have more designs and colorways than others.
Some manuf. (Benartex, RJR, Hoffman etc) have fewer total squares /strips, so you either get fewer prints or more duplicates, in my experience.

Moda charm packs have two of almost every fabric.
The total number is 40 pieces.
There were only 7 single fabric pieces in the last pack I bought.
Each of the Moda charm packs lists the color numbers on a card tucked inside the pack.

I hope that information helps.