Mixed S/N Font Star Bill

it is possible that the ink on the one counter may be low as oppossed to the right side counter.
It is common on CDN bills where some digits appear bolder and in some cases the numbers have been ink filled like a 6,8, or 9 digits.
I received a fresh brick where about 100 notes had this problem (roughly 1 bundle) until it was corrected where the rest of the notes where fine.
As for the letter fonts to me they look the same but hey at my age I could be wrong.
In some CDN notes there were letters in the prefix where the letter B was of different font and size. But this is rarer.
If is a known error check with a dealer.

Your title had me hoping you found a mismatched serial number. I've been looking for one of those in circulation for years. I figured it has to be on of the most overlooked, extremely valuable errors out there.

It doesn't look like an error