a handy reference is the Record guide from goldmine which has a section in the front which lists most of the labels and explains which ones are from which dates such as capitol -rainbow green orange red etc. available at most book stores Barnes and Noble for ex.
How to tell dates of Blue Note records?
I've recently begun collecting Blue Note records and love the sound of them. However, its difficult for me to tell the difference between the originals and the multiple re-issues. Is there a rule of thumb or guideline to telling which records are from which era?