My DD, now 16mo, has been 'sat' on a potty from about 8mo when she was regularly moving her bowels at the same kind of time each day (after breakfast and dinner) and for her 'waking up wee'. It's saved me lots of wet wipes in cleaning up nappy squished poo!
She started nursery (4 full days/week) at 11mo and initially they were also very good at managing to catch both wee and poo on the potty. More recently she's been getting a red bum crack as she's obviously pooing in between the two hour nappy checks.
The thing is she makes a massive squirmy "poo face" before one is due to come out, so I know to rush her to the bathroom. Shouldn't her nursery nurse be looking out for that kind of sign too? Just wondering.