These are apparently the same word with different kanji usage, but I was surprised to find today when I was learning 丹 that 丹精 is the far more common way to write this vocabulary. Is there a reason WK doesn’t use this version?
N-gram sources:
Google
Kyoto-Melbourne
Thanks for the feedback 
I’ll bring this up with the team to see if they’d like to make any changes to this, we’ll let you know what they say.
Hi again! The team looked into this and said that they are planning on adding the vocab word 丹精 in the future. We haven’t decided yet what we’ll be doing with the vocab 丹誠 but we’ll keep you all updated on that at a later time!