Doubtfire engraved loads of portraits for banknotes and they're all quite stunning, maybe especially so the variety of portraits of Queen Elizabeth II. When you have the opportunity, have a closer look at the Elizabethan portraits on the New Zealand banknotes of 1967. They illustrate perfectly how much work can be involved, and how, back then anyway, artistic arguments could still win the day over financial ones!
You see, the thing is that the higher value banknotes were larger and so is the portrait on them, but Doubtfire had only engraved the small portrait. As a time and cost saving measure, DLR tried to enlarge the portrait photographically and subsequently etch the larger version. This did not work out well, though, so Doubtfire was called in again to try and patch up the large portrait, but that, too, was of no use.
The problem is of course that a larger portrait needs differently spaced lines. If you just enlarge the smaller version, the lines will be spaced too far apart and this distorts the whole engraving. And so, in the end, Doubtfire had to engrave a whole new larger portrait as well!