15 year removed rule

NCAA rules only allow 37 numbers to be used (0, 00, 1-5, 10-15, 20-25, 30-35, 40-45, 50-55 with 0 and 00 not able to be used at the same time). Teams do have to be very careful about forever pulling numbers out of use. A player may only play with 14 other teammates in any one season but may play with three or more times that many through a 4 or 5 year career.
 
ISU currently only retires jerseys not numbers.

It's a matter of semantics. While it is the "jersey" that is retired, the number on that jersey has rarely been re-issued, if at all.

Hoiberg was the last to wear #32.
Grayer was the last to wear #44.
Hornacek was the last to wear #14.
Nobody has worn #35 since 1995.
Only one player wore #20 after Thompson (Eli Parker in the 84-85 season; switched to #21 the following year).
 
It's a matter of semantics. While it is the "jersey" that is retired, the number on that jersey has rarely been re-issued, if at all.

Hoiberg was the last to wear #32.
Grayer was the last to wear #44.
Hornacek was the last to wear #14.
Nobody has worn #35 since 1995.
Only one player wore #20 after Thompson (Eli Parker in the 84-85 season; switched to #21 the following year).
Which is why I don't think it is a big deal that the number is not officially retired. Once you go down that road it is difficult to back track and after 200 years of Cyclone basketball they may need to be using numbers of players who have had their jerseys retired.

Besides, I was replying to a post that was talking about how UNC does it differently and only retires jerseys unlike ISU. I was simply pointing out that it was more like ISU than unlike.