In this area it's been almost 20 years since any show has asked for a coggins test--in the late 70's we needed them to show at any of the rural fairs, but by the early 80's that was dropped and by 1988 even the breed shows quit making them a requirement.
A health certificate really isn't worth the paper it's written on. I know someone that just went & got health papers on some horses--vet gave them no problem, the horses had nothing noticeably wrong with them, but then the horses get hauled home, unloaded, and one is coughing & blowing out snot. One or two do the same when worked. That health paper is good for 30 days--so by show time the horses may very well be healthy & non-contagious. Likewise one of the others which was 100% healthy at the time the paper was signed could be full blown sick when it arrives at the show in 10 days time...
I don't blame any farm for not staying at the show overnight or however long they're supposed to. The local fairs here always have the rule that horses must arrive on the grounds by 8 a.m. and stay until 5 p.m. or until the last class of the day has been completed. We have never done that. For years we'd haul our yearling & 2 year old horses for halter--we'd show in our classes then pack up & come home, usually by noon. There was just no way we were going to sit there & wait through all the saddle & harness & draft classes, how pointless is that? At one time the monetary prizes were mailed out after the show; in spite of the rule that any horse leaving the grounds early would forfeit their prize, we always got our prize money. Now the prize money is paid in cash when the ribbons are presented, so there's no problem collecting the prize money & leaving early. Obviously they want the animals left there on display for the spectators to view as they walk through the barns, but obviously there is never going to be a show where ALL the exhibitors remove their horses. Here if 10 of us leave early with our horses, there are another 75-100 exhibitors that stay through to the end of the show.