Easiest way to check is to look at the details of your posts rather than just the number.
Click on "paid to post" at the top of this page; and then on the green link in the middle of the landing page and finally click on the link below the number of posts you've made this month.
There you will be able to look at the links that make up your posts this month. If there is a difference in the count, suggest you send a ticket to support to check it out.
I'm sure that if the list shows less than the number you're looking at, it's the lower count that will be used to determine whether you have 30 or more posts.