" At the end of the month you will have learned certain pieces, and others you will be still learning. The learned pieces are replaced by new pieces. The others go on to the next month. You must wait until the end of the month to replace pieces, even if you have learned them in the first week. "
But I am still confuse.
it was always aimed to bringing it to such a level that even if you let it be for some time ( say 6 months) your PPI will still be working on it. I don't think a week's worth of study to learn it up to that level would be sufficient.
first, even if you learn a piece in the first week or two, you'll have it ingrained even more at a months time. This way you also know the minimum amount of time you would have spent on one particular piece. #2 what i'm guessing is the real reason, organization. It's easier to organize 100 pieces over a certain amount of time if you only add/replace once a month.