I think we're talking about two different things.
1. There were no seats in the SEZ last season or the season before. There was standing room. Ergo, any seats that are there this season did not exist last year.
2. Up until about 10 years ago, give or take a few years, the official capacity of the stadium did not include standing room. This is why some Hawkeye fans ridiculed ISU for saying its attendance was more than 100% of capacity. I don't know if the school started including standing room because it was told to do so by the NCAA or if somebody just decided to do it, but that "increased" the official capacity.
3. They did have a cap on standing room. I do not know what it was, but it shouldn't be too hard to figure if anybody thought it was worth the effort. I'd guess it was around 14,000 for both end zones. There were games when it was impossible to buy a ticket; ergo, there was a cap on the number of standing-room tickets sold.
4. The number of tickets for sale this year is larger than it has ever been by about 4,500. This is obvious from the official capacity number.