Help with comparison of sheets

First time poster... Thanks for help in advance!
I have a large data set that gets pulled from another program into excel. Right now, its around 2500 rows with appx. 38 columns.
The data is taken from "Master" and sorted into 8 other sheets by the different people in my office in this workbook. I now have a total of 9 sheets. The 8 sheets are "worked and edited" except for a few columns; one of which is a master part number we use.

As time goes on, the original data is going to have rows added to it. Specifically a new part number is going to be added. However when it is pulled from the SW program we are using, the new data is going to be intermingled with the old. This data set is going to keep growing. I am trying to find a way to take the "NEW MASTER DATA" and compare it to the "OLD MASTER DATA" and have it spit out just the new data. Here is part of my problem... the part number we use is formatted oddly... "x xxxxxx xxxx x xxx xxx" .... I know I'll have to use the part numbers as a reference point... I just can't seem to figure it out. Suggestions?

If I provide additional information, would that be helpful?

Am I explaining this well enough?