Part Number Confusion - PDFs vs. Inventory

Hi folks. I can't find any reference to this in the forum using search, so I hope it's not a repeat question. Here goes...

I am in the midst of a complete inventory of my daughter's smallish collection of Lego. Primarily, I am trying to identify which bricks are "loose" so I can create my loose bricks list over at rebrickable. So as I'm going through the step of comparing PDF part numbers with set exports to find missing pieces from the export, I have noticed quite a few instances where the PDF part list and the inventory export don't list the same part number for the same part. For instance, in set 60018 I have the following in my spreadsheet:

Inventory Export: 6022452 (Mini Upper Part No. 1160)
Instructions PDF: 4275841 (Picture of bright blue mini figure upper part)

Or, for a more clear example, set 5508 has a White 2X8 Brick listed as part number 300701 in the instructions PDF, but the inventory export shows the part number as 6033776.

To me, this makes no sense at all. Why the discrepancy? Did Lego update their part number for this mini upper after the PDF was produced? Can someone help me understand this one, please?

Thank you in advance!

The_Iveys