You'll notice several cast-in numbers/letters/symbols on the different pieces of each full rocker box set.
Year Code:
The year code is a circle with the last two digits of the year in the center and 12 “pie slices” cast around the year code.
Some of the “pie slices” will have a dot cast into it. Count the number of slices that have dots in them to find the month the part was made.
I.E., in the middle section below there is a circle that has 8 slices dotted and a “94” cast into the center representing August of 1994 production date.
Then look at the other corner of that same side which also has a circle cast into it.
There are 6 “pie slices” around the number “4”.
So it appears this middle rocker box was made in August of 1994.
The 4 in the day chart may be a control number as 8-4-1994 was actually on a Thursday (Monday seems to be marked in the pic below).

Date codes on 1994 Sportster middle rocker box spacer 1)