J, C, D, Z, and P classes are all business class revenue buckets. R is only certain kind of upgrade bucket.

J is fully flexible.

C, D, Z, and P are less than fully flexible.

Within each bucket there could be many different fares offered at many different prices with many different conditions. The airline will offer as many of each bucket as they feel like, presumably based on how many they think they can sell.

The number of business class reservations they permit on one airplane is also related to the number of economy class reservations there are. If there are more reservations than economy seats they know they can put people in business class seats.

So a "few days" ago they were willing to make 5 more business class reservations, all at full fare J, because of some combination of existing business class and economy reservations and any other information the airline (thinks it) has.

Yesterday things had changed so they offered three more reservations, with one of them in either C or D.

Today things changed again so they offered at least one more reservation and three more in C.

What might have changed? People may have cancelled or changed their business class reservations, or their economy class reservations, either of which would change the airline's belief in the number of people who are going to be sat in business class. Other things could have happened as well.

I can't remember the upgrade details. I don't play that game anymore.