You probably already know the percentage of sales of items by category that are new in the past year. The table looks something like this (here, I had 5 years of purchase history so the 4th-5th year is not applicable).
Here we see a brand in disarray. Look at Category 2 ... somebody decided that newness was important last year. Look at Category 4 ... somebody decided there was too much newness and scaled back. Look at Category 8 ... pure chaos, nobody knows what the "right" answer is. Look at Category 12 ... the category is being slowly starved of new items over time.
This is one of those situations where you don't have a strong Chief Merchandising Officer.
You can tell when there is a strong Chief Merchandising Officer, because the differences by category are much more consistent than what is illustrated above.
Now, you don't necessarily need a strong Chief Merchandising Officer. Or, the measure of "strength" is wrong ... a quality CMO might let his/her underlings make independent decisions (if that is the right thing to do). But you have to know what is right for your brand, and then guide your merchandising team toward the right path.