DR question

[kelticpete]

So Hervy the druid is wearing armor that has DR of 10. and it has an added 3 reduction to pierce.

 

but when he got hit by a pierce from a beetle, it said the DR he had was only 8. 

 

a) is the number just wrong data? 

or

b) is some other factor lowering his DR? he had no negative effects on him.

 

just confused. 

[Rhaegar83]

Best guess is he got hit with something like a stiletto that has a -5DR property. 13-5 = 8

[kelticpete]

that makes sense. maybe the stone beetle can pierce DR.