Hi Susan
What I'm about to write dates all the way back to the earliest versions of ACCPAC Plus, and you wouldn't have guessed it until you read my words.
Comments (and instructions) are actually "attached" to the detail line that is just above. When an order is partially invoiced, any comments that are just below a shipped line will print, any others will not print (unless you choose to print unshipped lines). Those comments that are just below a shipped line will not print on subsequent invoices.
I believe that if you put a comment on line 1 of an order, it is not attached to a detail line, and will print regardless.
Does this explanation help you figure out what you have to do?
Steve