Most of the NPC sororities have a 6-8 week new member program. A school may require an even shorter program, to avoid hazing. Some chapters may hold over members longer to get grades.
When a chapter is having Continuous Open Recruitment they may decide, with permission from the appropriate National officer, to have a shorter new member period. This is so that the members can be initiated before the end of the quarter/semester or so that all members of the same class are initiated at the same time. It's a way to avoid "hold overs" and avoid losing girls over winter/spring/summer break.
Your experience is not common, but not it's not
that uncommon either. The important thing is you're an initiated sister. Whether you new member period was 4 weeks or 4 months (like in the 1940s/1950s) you still have the same privileges.
