What we do is have a fall and spring pearl class(since we can't call them pledges we call them pearls after one of our jewels). Anyway those that join in the spring are still considered members of the fall class- they are the freshman class. So at retreat when we break into groups -the freshman are all together- they are not divided by the semester they joined.
Now regarding COB once we did this all spring, but it is very stressful and i those that join later in the spring miss out on a lot of stuff. Since our new member program lasts six weeks we will cram it and have those that join late(which has only happend twice) come and meet with our New Member educatior. But no we do not have different classes based on COB's. That would be too confusing!!
i hope you understood what I just wrote!