The UNC System keeps good records
https://www.northcarolina.edu/sites/defa...port-3.pdf
Fall Census Counts:
1972 NC State 13K UNC 19K
1981 NC State 21.8K UNC 21.6K
1991 NC State 27.8K UNC 23.8K
2000 NC State 28.6K UNC 24.8K
2015 NC State 34K (24 UG) UNC 29K (18.5 UG)
Carolina graduated more kids than NC State until about 1995 or so. Carolina prides itself on making everyone graduate. NC State prided itself on how many they could flunk out until about the year 2010. This may sound like an oversimplification, but it's not.
It takes a long time to make up a 120,000 alumni deficit when you have only been making gains against UNC for the last 25 years and the difference has not been substantial until the last 15 or so years.
NC State was relatively small for a long time and with no medical, dental, nursing, law, journalism, or public health school that meant that quite a few NC State alumni, also became UNC-Ch alumni.
The numbers posted are 5 years old. In that 5 years NC State has added about 28K graduates and UNC about 22K. What is more significant is that Carolina's alumni are dying as a greater percentage than NC State's alumni simply because there were so many more of them.
I would estimate that NC State has gained an average of 2,000 alumni a year over UNC-CH over the last decade. In the fifteen year before that, around a 1,000 or so per year. That's a net of gain of about 35,000 over the last 25 years or so.