Oh, the confusing Peacocks!!
Millersburg had 10 patterns (with 9 separate moulds).
Northwood had 8 patterns (using 3 separate moulds in progression over time).
Fenton had 2 moulds and 2 patterns.
This Summary Table of Features (put together by Ron Britt) will assist you in identification. Quite frequently you can narrow it down simply by determining the diameter of the piece, but if you need more detail to figure it out – the information exists here. Do the peacock's tiara face forward or back? How many feathers are in the tail? Check it out here!!
NOTE that in many cases the mould used does not currently impact the price. It may in the future if it is discovered that one is much more difficult to achieve than another and someone wanted multiple examples.