As a general rule, in any of my adult classes, the non-Catholic baptized Christians are the most knowledgeable about Christian doctrine in general, the bible, the beliefs of their own denomination and Catholic belief. Some do run into intellectual roadblocks regarding doctrine, but most roadblocks are procedural (annulment etc). They also tend to make the most rapid progress.
Baptized Catholic adults are the least knowledgeable. They are also most likely to drop out and to be seeking Confirmation because they want to get married, and to have unresolved issues, usually regarding marriage, that delays their progress.
Even unbaptized persons generally have some knowledge because they have usually been befriended by a good practicing Catholic who has been bringing them to Mass and explaining things to them (and who often becomes the sponsor). The discernment of their conversion is the most challenging part of RCIA and where the pastor’s involvement is critical.
Since all 3 categories of members have to cover the same ground, and I am only one person, we have one class. When necessary and with the pastor’s permission we make other arrangements for someone with specific needs–schedule, college, work, travel etc. Never came across a situation we could not work with, including deployed military men.
We schedule interview with the pastor for all, and he is usually able to assess when someone is going to need more, or less than the full year class. For instance, a person who had actually been teaching CCD with her husband, was well known to the pastor, yet never formally embraced the faith, needed only a few conversations with myself and the pastors on some doctrinal points, some intentsive prayer and a retreat, and was received into the Church after only a few weeks. yet she had been preparing for 20 years, ever since she married a Catholic and resolved to learn about his religion, honor the promise to raise the children Catholic, and worship together.
If I have 10 people who begin the class at roughly the same time (we go year-round) it almost never happens that all or even most celebrate the sacraments at the same time. People just do not progress on a spiritual plane according to a set schedule.