Each boss has 25% chance to drop (20 minutes pop = 1,5 patterns/hour).

And you have almost 100% chance to have a piece of pattern if you wipe the entire camp (Hiathlin + Shadows) bringing your chance to loot @ 4,5 patterns/hour in average.

Pieces are cyclic. So you can spend 6 hours in a row and never see a C part. Then, after a pause, 4x C in a row are dropping. Then A, etc.

After 36 hours of camping, i had more or less the same amount of pattern for each piece. To say there is a hard piece is a wrong sentiment.

Is it helpful ?