Looking at the change log, it would appear that you did them one by one.
On the "Inserts and Related Sets" page, if you click on the pencil "Edit" icon to the right, it brings you to a page with several options. One of them is "Update All Notes". From there you can choose "Find/Replace" and enter "SN" in the find field and "PR" in the replace field and the system does them all almost instantly.
-Tom
Ted Musgrave card collection 98.9% Complete: Cards Known: 1013, Cards Owned: 1002
I prefer the company of people who disagree with me for the right reasons over the company of those who agree with me for the wrong reasons.