Hello to all.
Funny case was today. I had try to recover data from one 4Gb flash drive. There were one chip with stack structure (2x2Gb stacks, I knew it). When NAND chip was inserted in reader, I see in my program 4x2Gb dumps!

I was shocked!

I took out chip and clean legs. It really help! When I insert it again programm shows me 2 dumps, and it was right.
Conclusion:
It's neccessary to clean legs in all cases with NAND chips.