This is more worthy of a comment (I don't have enough reputation), but in the math / statistics community, independency gets an inordinate amount of use.
On their own, Google shows that the "Independence" keyword is used ~500x more frequently than its archaic counterpart. However, when you add the keywords "Math" and "Statistics", it is only used ~50x more frequently. In fact, nearly 50% of the references to "Independency" also contain "Math" and "Statistics".
In this context, we often see independence used as a possessed quality, and independency used independently of possession:
- We can verify the linear independence of x and y.
- Every independency contributes to the sparsity of the problem.
Even in this field, they are often used interchangeably.