Here is Plus Box #3. I think these were made from about mid-1988 onward.
The Plus and SE had some changes that year. They lost their specs on the rear bucket label (no more "Macintosh Plus 1MB" or "Macintosh SE with one 800K Drive and 20SC Hard Drive"), the copyright dates were updated from 1986 to 1988, and the manuals would have changed to reflect System 6 (I have a Plus manual from 1987 which clearly has System 4.1 depicted). The style of labels on the floppies changed in 1988 too--no more black stripe on them.
The Plus and SE had some changes that year. They lost their specs on the rear bucket label (no more "Macintosh Plus 1MB" or "Macintosh SE with one 800K Drive and 20SC Hard Drive"), the copyright dates were updated from 1986 to 1988, and the manuals would have changed to reflect System 6 (I have a Plus manual from 1987 which clearly has System 4.1 depicted). The style of labels on the floppies changed in 1988 too--no more black stripe on them.