i doubt it -- after all, it has to stored somewhere and as far as i understood the flashing and the layout, flashing rootfs and emmc(?) will effectively replace _all_ content with the default data from the images.

as said before, your results of the grep oneliner are rather confusing and to me (w/o any deeper knowledge) it looks like there's something wrong with your /dev/mtd1.

as for the '*' as result of
grep -A 13 lock_code /dev/mtd1| tail -4 | head -1
try playing around with the values given to head and tail (4 and 1) -- it does only read, so no risk. my guess is, that the diamond shaped symbols are the string you are looking for.