Texas Graduation Rate is not 88%!

The Texas Education Agency is claiming that in 2013 Texas had a graduation rate of 88%.  The errors in that claim are rather clear as stated by Bill Hammond in this article: http://www.texastribune.org/2014/08/05/texas-posts-top-high-school-graduation-rates-again/

They are claiming that this is the highest graduation rate in the US due to the chart they quote in this press release today: http://tea.texas.gov/About_TEA/News_and_Multimedia/Press_Releases/2015/Texas__high_school_graduation_rate_for_Class_of_2013_again_exceeds_national_average/

The only problem with this claim is obvious when you look at the enrollment by grade patterns over the past decade for Texas:



Texas Enrollment by Grade 1997-2014
Click to enlarge image.

Notice the Promotion Rate line above in the chart, 5 lines from the bottom.  Yes, Texas has made constant progress, but when only 79% of 9th graders are even making it to 12th grade, how do you have a graduation rate of 88%?   

When the Cumulative Promotion Index, the last line, is only also 79%, how can you have a graduation rate of 88%.  As multiple people are saying, this claim does not match with the data.