Mobs will always drop items with the same sequence on the same seed, but this does not apply to the durability level of natural equipment. To reproduce:

1. Use the seed -6365024550271055859
2. Spawn drowned until you find one holding a trident
3. Kill the drowned holding the trident
4. Repeat steps 1, 2, and 3 in another world
5. Notice that tridents from the same seed and sequence have different durability