Every album needs a cover, and every cover needs to be designed, and with Sgt. Pepper it was no different. From what I can gather a new album cover design needed to be created for Sgt. Peppers and the task was set upon.

The next paragraph is purely speculation and my educated guess as to the Fourth Proof origins.

In my opinion it appears that at least four possible designs were created for EMI to check over to see if it fulfilled their requirements. Each of these designs were stamped with the internal catalogue number (for easy retrieval) and the designers initials. Each also had a proof mark in the corner to distinguish the designs apart. When the design was selected Garrod and Lofthouse then went in and started to produce the sleeves ready for when the album was to be released in June. However, the production print that told of the proof number and internal catalogue number were accidentally left on and a batch or two cover were printed before it was discovered and the text was removed.

I have compared my standard Sgt. Peppers sleeve along with the Fourth Proof sleeve and visually they're pretty much identical bar for the additional text and extra lamination as highlighted in the Closeups section. Although the only real differences between a Fourth Proof and a standard sleeve is minute at best, the Fourth Proof sleeves are incredibly difficult to find, and are held in a very high regard to collectors. If you wanted to buy a top-quality one don't expect much change out of £250.