Exchange 2007 Rollup Update Issue

I have a customer that is running Exchange 2007. After applying the PS commandget-exchangeserver | select name, admindisplayversion it indicates that it is running at Version 8.3 (build 83.6). When I look into the installed updates it shows that all rollup updates up to 18 (8.3.459.0) are installed.

How can we fix it so that it is running at Rollup 18?

Thanks