We have ended up spraying glyphosate in some fields this year multiple times. In many cases it was not planned. The problem is, when you are trying to hit one leaf grass weeds, there are not many suitable spraying days when you can use flat fans. So what happens is you have a weather window and you think you might get to drill, so you spray. Then the weather doesn't quite play ball and drilling is delayed by which time some more has appeared. You're not exactly going to drill with a whole load of freshly germinated black grass which can be easily killed out of the crop, so you spray again with the hope of drilling once the rain stops. The rain doesn't stop, and so you are into a spring crop. Then the process happens again.
One of the reasons I prefer to spray after drilling, there is always a window even if sometimes it might be a 2 am !
Does depend on a low disturbance drill though