If I wear two Plunderer's Ring, does the effect stack?

Solution 1:

According to this discussion:

LCK = chance to find items and chance to land critical strikes

LCK might also affect Shard drops.

I think luck has 2 functions with it. 1. Definitely effects drop rate of rare items such as Armor and Weapons. 2 I think it has to do with critical strikes

And when someone asked for the best weapon drop build in this discussion the kit suggested had two plunderer's rings

Best armor set for LCK: Ribbon Kalasiris Plunder ring Plunder ring Bunny scarf Augment Luck yellow shard maxed Augment Luck white shard Eat all foods that give luck

Both of these discussions are from the bloodstained community and not actual an official statement, but I think it's safe to assume that when you see your LCK increase with each ring then drop rates are also stacking, because that is what LCK represents.