I've lost count of the number of parades/march pasts/Guards of Honour I took part in during my 25 years service.
The cocks up's were stunning. A few memorable one's;
Parade Commander who totally screwed up the running order of a Freedom of Doncaster parade and marched us into a cul-de-sac.
Route lining at East Retford, having to Present Arms to a mayor (in full mayoral kit) who had forgotten to take his bicycle clips off. The SWO, walking behind us muttering "No laughing, no laughing" almost brought the house down.
Same year, AOC's parade. At the last moment somebody unearthed a bugler and thought it wold be a good idea to 'Sound the Advance' at the start of the proceedings. No-one had warned us of this. AOC lands, Parade Commander orders 'Sound the Advance', Bugler bugles and one very pissed off FS shouts 'Charge', parade falls about laughing.
The whole of the OR's at Linton being marched (5 times) in front of the hangars on a very warm Friday evening because the JP Flypast Leader couldn't get the TOT right. That farce only ended because the jets were running out of fuel. (Oh, and having to march past the Studes crewrooms whilst they sat on the grass and drank beer. Good for morale that was).
Oh, I could go on.
The point I'm trying to make is that no matter how much rehearsing is done...........