I've never really taken a look at this portion of books before, but obviously, it can be a very technical detail.
Here is Wikipedia entry on the matter:
Now, take for example the following image:
What is the classifcation number?
Is it PZ7.M5685 or is it PZ7.M5685 An 2000?
I would list it as PZ7.M5685 2000
LOC record states it is the full PZ7.M5685 An 2000