Hi Andrew --
This is an error corrected in another thread titled "Official Errata". Copied here for your reference:
Section 3 - Setting up for Play - Card Preparation
Step 2 should read: "2. Place your initial supplemental cards in the Available Supplemental Cards box."
Step 3 should read: "3. Place your German reinforcement cards in the Cards Entering Play box."
Section 4 - Sequence of Play - II Card Preparation Phase
Step 3 should read "3. Place all Supplemental Discards from the previous day face down in the Available Supplemental Cards box.
The Daily SOP on the back outside page shows this correctly - as does the German Command Display.