It's standard procedure to count change order work as revenue on WIP (Work in Progess) especially when you know that you're going to eventually collect. Most change order work is done with a Request For Change that is agreed to by the owners. However, it can take month before a formal Change Order is issued. The money has been earned, the owner has acknowledge and approved it, but the formal paperwork takes time. Also, there is nitpicking over the final price. It's not usually very large but it's sort of tradition.
When a change is requested, it is frequently agreed that it will be performed on a cost plus basis.
Nothing to see here folks, this is standard for the industry.