You don't put your clean up bull with the cow until at least 30 to 45 days after AI'ing. Then you wait until the birth, to see which bull is the Sire.
However, good vets can ultrasound a cow after 25 days and tell you if she's bred or not, so if you want to try AI'ing again you can do that first.
If we are AIing with say a maine and we are using a Brahman for a clean up bull then the difference is obvious. However if we are AIing with an angus and cleaning up with an Angus then we wait 30 to put them with the clean up bull.
Typically a cow/heifer is our of standing heat by the time she's AIed. Even if she is still in and just going out, if you wait 24 hours she won't be bred by the cleanup bull till the next heat cycle. A vet can tell by palpation that 3 weeks difference. If he/she/it can't, time for a new vet. Plus she will generally calve later to the cleanup bull. But, there are alwasy the cows that are w eeks late or two weeks early.
A friend of mine used to use an Angus bull then a Hereford for cleanup. Not much chance of getting that wrong.
With our Longhorns...color & size doesn't matter...lol. Calves can be any color. When we A.I., we wait 2 cycles before putting female with clean-up bull. If really a critical breeding, we'll have her palpated in 2-3 months.
We keep watch of the cattle and write down when bred either ai or natural. We have kept records on the cows since the seventies and know which cow families tend to go over versus the ones that normally calf a week early.