This is a distillation of a discussion that several costumers contributed to. These are general rules that most experienced costumers and masquerade judges agree on.
When trying to document a costume for historical or re-creation purposes, assume that:
"Pictures of any kind are good. I took photos of the process, and of me wearing the chemise, the corset, etc., so the judges could see what it all looked like. In addition, I had one page where I glued swatches of each fabric and labeled it."
"I often do detailed documentation even of SF and F costumes, especially if it is a figure from mythology, or if I am doing research on the costume "profile," such as I did for the samurai. Even though it was a fantasy samurai (rather than any sort of historical samurai) I wanted to demonstrate that I had used examples of the real thing to formulate my own designs."
"Workmanship judges often appreciate this."
If you do something different from actual historical, be sure to document what it is and why. Legitimate reasons can include: