Unless you are citing a comprehensive list of women who have been raised, we don't know jack about what the Tower was up to, regarding raising women, at any given time. They slipped a sister's rise past us during the series with little fanfare, so we can't even be sure how many women were raised even in the one place for which we have the most detailed data.

If you are citing a list or something from RJ's notes, that would be an okay point at which to jump off. If this list is backfilled from among the entries in the Companion, then the data is useless. It does not tell us that six women were raised to the shawl in 979, it tells us that six women who appeared in WoT happen to have been AMONG the women raised to the shawl in 979. For all we know, there were thirty such women, who simply did not play any role in events 20 years later.

We could use this to analyze what that might say about the involved women, that so many of them came from a relatively recent period, but it tells us nothing about the Tower, any more than the 13 Most Wanted list of Black Ajah which Verin gave the girls in tDR told them anything about the actual Black Ajah itself. And for much the same reason. As Elayne & co allude in their discussion of the list, it seems like they were deliberately chosen from a wide array of demographics to conceal any possible patterns in the membership. Likewise the women who appear in the series tend to appear for specific reasons, suggesting it is just as unlikely that they are a representative sample of the Tower. For example, it is said that a good third of the sisters were staying neutral during the split, but aside from Cadsuane and her faction (which could be as much her doing as their own inclinations), and maybe Amylia, we don't know any of them. Based on a census taken from the entries in the Companion, one might conclude that only a tiny minority of sisters were neutral during the split, since most women are listed as belonging to the rebel or loyalist contingent.

Of course, if you have another actual source, that's something else. Do you?