Muldrotha, the Gravetide is on the battlefield:
During each of your turns, you may play up to one permanent card of each permanent type from your graveyard.
I play Spark Double:
You may have Spark Double enter the battlefield as a copy of a creature or planeswalker you control, except it enters with an additional +1/+1 counter on it if it's a creature, it enters with an additional loyalty counter on it if it's a planeswalker, and it isn't legendary if that permanent is legendary.
Since I now have two creatures on the field that say I can play up to one permanent of any type from the graveyard, could I play up to two permanents of any type from my graveyard? Could I, for example, play two creatures instead of one during my turn? Or am I missing something?
The rulings only mention other effects that allow me to play additional permanents from the graveyard, but they don't address the same effect:
4/27/2018. If multiple effects allow you to play a card from your graveyard, such as those of Gisa and Geralf and Karador, Ghost Chieftain, you must announce which permission you’re using as you begin to play the card.