Still on my way up a learning curve.
Im familiar with the C8 family, aware of the A6, and think I know about the Nl40 size. I'm sure there's more I don't know.
Does there exist any kind of list that defines the different form factors of lights?
slmjim
What do you mean by form factor? Flashlights are often either straight body or a right-angle. Also their overall size is influenced by the size and number of cells they use. Furthermore you have to consider the general purpose of a light. Thrower type lights such as the C8 will have a large reflector whereas a A6 is just like a straight tube. You can use a site like this to help you search for flashlights with given features:
Mmmm, not really what I'm looking for. It might not exist.
Im thinking the C8's, for instance, exist within a certain reasonably narrow range of tube & head sizes, depending on cell & cell count.
Is there an alpha/numeric descriptor that is shorthand for certain general designs and sizes?
For example, Is there a number/letter descriptor associated with soda can lights?
slmjim
The C8 is available from a few manufacturers however generally each manufacturer has their own naming conventions and their own unique flashlights models.
Not really. You can try searching for lights with 3x or 4x 18650 capacity. However there are also very powerful thrower lights that may use the same configuration.
If you are looking for a Rosetta stone, as far as I know, it does not exist. Depending on what you are looking for, searching through the forums can be quite tedious. The folks in here are generally quite friendly and helpful, so I recommend asking for suggestions if you are looking for something specific. The more detailed your question, the better your results will be. For an example, here is a suggestion request I recently submitted: Recommendations for an 18350 powered RT angle Headlamp/Flashlight
Good luck!