1999P 25C Missing Letters 0

[MRLAUB]

Here's another weird one where I'd like to get all of your opinion.  This coin is well circulated.  However, you'll see the "I" in Liberty and the "E" and "T" from IGWT missing.

I'm assuming this just gets worn out due to circulation rather than some odd mint error.  

I'm trying to learn as much as I can about mint errors.  Thanks!

[RWB]

Not wear, but more likely filling of the missing letters in the die with metal fragments and oil. Interesting but not valuable.