I think everything I looked at when shopping around said blend on the bag. I don't know the exact answer as what the actual blend is. My guess is the mill that grinds it just can't guarantee purity. Otherwise they would have to constantly clean their equipment and inspect for "strays".
What my Loews has
As I'm filling cages I look for odd pieces. The only odd piece I have ever found was some bark that looked like pine. I'm not familiar with Cypress bark,except for the kind in rivers and swamps which looks different. Maybe "inland" Cypress bark looks like Pine bark, I don't know, but suspect so.
Bottom line is, neither me or the breeder I know has ever had safety issues.