Can an ordered array inside a document with MongoDB be guaranteed safe to maintain order in production

Question

MongoDB maintains order in arrays within documents. If order is critical to that collection and particular project, can that default ordering be guaranteed safe to always maintain its order? Or should explicit ordering property be implement?

ie

someDocument: {
  orderedItems: [Items]
}

vs

someDocument: {
 orderedItems:[{orderNumber: Number, item: Item}]
}

Production level means millions of transactions depending on that data, as well as mutations on that list ordering occurring.