Here in Oklahoma, we nominate in mid-October for the OK Youth Expo in mid-March. The ag teachers and county agents are responsible for overseeing this process for the exhibitors under their jurisdiction. Each nomination consists of a nose print, DNA sample (hair pulled out, supposed to be at least 60 hairs, most take it from the tail (but not the switch)), and two photo's clearly showing the calf and exhibitor together, one head shot, and one side view. Official eartags are to be put in at this time. We send in the information required by the state breed association for classification, their representatives are given this info and allowed to review the pics, and this constitutes the classification process. If more than one eligible exhibitor resides in the same household, the other exhibitor's name(s) may be listed on the outside of the envelope, and any of them will be eligible to show the steer. This allows a family to nominate an extra animal(s) in case something happens to one of them, or to allow a family to wait 'til they enter at the show to decide which exhibitor shows which animal. Once an animal is entered in an exhibitors name (in February) and that exhibitor becomes ineligible, that particular animal becomes ineligible, so that the ineligibility rules can't be by-passed. If, for example, 3 siblings have 5 steers properly nominated and entered, and all 3 are eligible at show time, any one of them may show any 1 or 2 of the steers. The same family nomination rule applies to all species of market animals. An exhibitor may nominate as many animals as they wish (I'm pretty sure) but may show a maximum of 2 steers and/or 3 each hogs, lambs or goats. An exhibitor is only allowed one animal in the premium sale (maybe with the exception of multiple grands/reserves).
This, or weigh in for our county performance contest (which happens about the same time, and consists of a weigh in and a tattoo in the steers ear) qualify a steer for the county show/premium sale, which is around the 1st of March. The same numbers limits apply as OKC.
For the Tulsa State Fair (which is in early October) there are two locations (sale barns) where the steers have to be taken on particular days (in early May). They're weighed, tagged, nose printed and DNA collected (sometimes hair, sometimes blood) and representatives from the state breed associations are on hand to classify. I don't think Tulsa has the family nomination option. Again I believe there's no limit on nominations, and an exhibitor can show up to 3 market animals of each specie, but can only sell one animal.