Hi Scottie,
SP4 Patch3 would include Patch1,2. But in some rare scenario, there are fixed on Patch 3 which unknowingly might break the fix of Patch1,2. We call it as regression. So, it is likely that at time if the issue which was fixed on Patch1 and reoccurred on Patch3 might be due to regression.
Let me know if this helps in understanding.
Also, as per your query on the blog I wrote, let me know if you were able to just this on sandbox or test system. You can just downgrade the client to Patch1 and test. The patch can be again updated to 3, but this would confirm if there is a regression.
Hope this helps.
Regards,
Amit