In addition to explaining about 'hanging diamonds' Reggie mentioned in his answer to me, Meisterin Katarina Helene also pointed out to me that the process of using an overlay to check an example of my work with the original that Reggie suggested was actually the opposite of 'the normal' or 'natural' way you'd check.

Naturally, you'd overlay your work on top of the original.

Reggie recommended that you do it the other way around - having a transparency in red lettering of the original and laying it over my work and "the differences will jump out".

He also said "very importantly, take any piece you do and hold it up to a window so the back side of the paper is facing you. This truely helps you to see your work with new eyes: very important if you are hard pressed for good critical input."

I know about looking at it upside down, but I'll give looking at it in reverse as well in future.

Meisterin Katarina Helene also suggested :
"Another trick you might try is to make very pale copies of Drogin, and then use a color wash in your nib to trace over them, or place a piece of tracing paper over the copy and then trace them with your own pen in another color. This helps you train your hand in forming the correct shapes."

.....which would be good for when I'm starting to learn the Bedford Psalter ductus for some of the more complicated letters. (like the weird G)