Hello Wallace,
Actually, there are many of these mentions.
They are in a rectangular box at the bottom of pages, starting 0-3/1 Technical specification
Some say Modification Oct. 67, others April 67, some February 68. They are all over the book on many pages. Some say 'Supplement', others say 'Modification' while yet others say 'Changes'.
I had never noticed these before your question!, so no, not a dumb question.
See photo for print in BBB