Your system marks an item as posted as soon as it is called up and copied to Instagram. However, there are many reasons why an item would not be posted yet despite being pulled up this way. For example, today I pulled a post up and realized I needed to edit it. I went back to Later, and the item was greyed out already, as it had already been marked posted. I had to make a whole new post. It was not posted yet, and I should have been able to edit at that point.