Generally we do see all our sheep and all our cattle - in fact, all our livestock - every day; all 800+ of them, spread over an area 2 miles long by a mile or so wide. But it's our job, we're full-time farmers.
When I was on the moorland farm - 1000 acres of mainly moorland, carrying 530 ewes and all their 800-ish lambs - we also saw all the sheep every day. It sounds impossible but you soon get to know where they hang out, and the collie dogs run about and alert you to any sheep skulking trying not to be seen. Of course, unless you are feeding them every day, so can count them as they eat in a line, you can't get an exact count of many hundred spread over 500 acres, and collie dogs notwithstanding, there will be the odd casualty you never find, or don't find for several days - or even longer.
I see my neighbours zipping about on quad bikes and buggies, and have no reason think that they all do anything other than check all their stock every day, too.
If we were in a more fly-prone area, I couldn't cope with not seeing everything every day. In fact when we do have a spell of those sort of conditions, we generally check the most vulnerable groups twice a day.