Standardized tests that have been around for decades, such as the SAT or Stanford-Binet, are often renormed so that the number of questions needed to achieve the same score changes.
Why are standardized tests often renormed?
The tests have been revised to be more subjective as expectations of test questions have changed.
Tests are now scored by computer.
There has been a major trend towards using only verbal measures on intelligence tests, requiring a renorming.
Standardization requires that questions have been piloted on a similar population as the people taking a test, and the demographics, knowledge, experiences, and intelligence of test-takes has shifted over the decades.
Because of the Flynn Effect, scores on intelligence tests are going down.