We were discussing the World of Greyhawk portfolio edition on a Facebook group the other day. According to the page for it on here, the only noticeable differences is:

"...
Folio cover:  Wizard logo, "World of Greyhawk" is in a messy black calligraphy font.  "1980, TSR Games" on bottom right appears to be stamped, not printed, and is slightly higher (about 1cm) than on the next two prints.  This is the only feature distinguishing this print from the Second print
..."

I broke out my notes and saw that the first printings that I have owned have all had the letter I in the "1980, TSR Games" where the second prints and later have the number 1. The other note I had was that the dashes separating the ISBN numbers were slanted up versus being straight across on the second printings.

A few of us came to conclude after looking at the first prints that we own/have access to, that the first prints do indeed using a letter I in the 1980 date and the dashes do slant up. Can everyone that has a copy of a REAL first print verify this information?

I am going to try to upload two images showing these differences. Hopefully it'll work

Now that I see them side by side, the font used is different too. Look at the numbers 3 and 5 in the ISBN. In the first print, they have little hooks at the bottom loops where they don't on the 2nd prints and newer.

The first print, which was hand stamped, is so very clearly different than all of the prints that came after it, which were not hand stamped. For the reasons that GreyM is pointing out and that sometimes the stamp fades out a little, since it was hand stamped. The reference to being 1 cm higher should be gotten rid of in the Acaeum description. I can only imagine that was someone's anecdotal commentary from the distant past.