OED and NED (corrections?)

Hello there

Since some time i am interested in the "Oxford English Dictionary" and
its history. Especially the differences between the "original" "New
English Dictionary" which appeared in 1928 and the re-issue from 1933,
called "The Oxford English Dictionary".

The title of the 1933 edition says, it is a "corrected re-issue"!
But if i have a look at both editions i can see no difference between
them
except the number of volumes (from 10 to 12), the general appearance
(color etc.),the missing prefaces of the single fascicles which
constituted the 1928 edition and other little things.
But if i take a look at the single pages and definitions, there is no
difference.
It seems as if the 1933 edition was printed with the same plates as the
1933 edition.
Maybe the "corrections" are just in the supplement to the 1933 edition?

I know that there are several book, dealing with the OED, but they do
not answer this question exactly...

Does anyone know more about this matter?

Thanks
Jan