A friend has asked me to revive their peace lily given to them last Sept. Half of each leaf is very dark in colour. Soil is moist. The pot is approx 10 inches high and about 8 inches across at the bottom. There were no drainage holes in the bottom of the pot so drilled 4 holes.
Drainage in a potted plant container is crucial, so you have certainly helped the plant by providing drainage for excess moisture.
Here is a link to refresh you on the care requirements.