Typical bad block counts

[Dave Kelly]

On a 1Gbit single level nand (ST-micro), I have 10 chips all with less
than 6 blocks that are bad originally, a few with none. 

The chips all bit flip excessively in a few blocks.

I am suspicious that somebody erased the original marks. The few blocks
with 0 for the bad block mark all are stuck on 0 for the entire block,
so could never have been erased anyway.

What is a reasonable number for bad blocks on this size chip as it 
arrives from the mfg?

 
Thanks.