Those who were born before the millennium might remember a time before computers adorned every desk, even word processors were a rarity, and electric typewriters were the serious writer's best friend. Actually, that's wrong–Tippex was a writer's best friend. More than three mistakes on a page–tippexed or not–and you were advised to start again. Worse still, because you couldn't save your files in umpteen different places or print off a pristine copy whenever you needed it, you had to make carbon copies, use different paper for the under-copy (bank or bond? I don't remember which), and find space to store them. There was no spell check to help you either. This meant not only that preparing a manuscript for submission took much longer, but that you really had to pay attention and get things right first time.
    These days, it's much easier to produce a faultless manuscript, but you still have to take care, especially as different publications require different formats. Every time you change your manuscript you run the risk of making new mistakes e.g. leaving US spellings in a manuscript destined for a UK publication and vice versa. You can save the same text in different formats under different file names, but then you have to be extra careful if you edit it that you make the alterations to the right file.
    This was recently brought home to me when I discovered the code number I thought I'd saved at the end of the Smashwords edition of Discord's Child wasn't there. As a consequence, I've now put the code number for a free copy of Discord's Apprentice at https://www.smashwords.com/books/view/542490, and I sincerely hope that anyone who bought a copy of Discord's Child from Smashwords since Christmas uses it. Of course, anyone else who fancies a free copy, can also use it. It's valid until 1st March.
    I still have no idea where I actually put the missing code number, and probably never will.