If you miss your deadlift at your knees or around mid-shin height, it's common to hammer away at RDL's, good mornings, and other variations to train your posterior chain. This can be beneficial, but without a strong upper back those supplemental lifts won't do a thing.
That's why chest-supported rows should be a staple in your program when training for a deadlift PR:
Likewise, strong lats, traps, and rhomboids are undervalued when training your deadlift. Increasing their strength will ensure that you can keep better mid and upper back position during your pull, especially when the bar hits mid-shin height.