@ehBeth,
I breastfed both my kids. I did not get a period between pregnancies, of course till the one that got me pregnant... My kids birthday's are two years - less a day- apart. It's not really a great means of birth control, because, you don't know when your cycle will start again. It's a great big mystery, kinda like playing russian roulette. Generally, women that breastfeed don't get their period as quickly as women who don't, sometimes for many, many months after they deliver a baby - as in my case.
My milk dried up almost immediately when I became pregnant. Some woman can go for a couple of month longer into the pregnancy and some never stop. Some woman can't ever breastfeed, some only for a few days and some can do it spontaneously without being pregnant or using medication. There are even reports of men lactating.
I don't know of any studies that give the percentages of any of this, but I do not that your examples are not mainstream, not for Canada nor the world. The few women I've met that continue breast feeding till children have adult teeth, generally didn't have large broods. Usually 1 child, as it's hard to maintain milk for a family of five.