Mistakes happen. Mistakes happen in LARPS a lot. You're supposed to learn from them, and with luck your mistakes will be worth a couple of laughs. Here is a sample of the mistakes I've witnessed over my LARP career.
Time has an interesting effect on games. A historic setting is sure to confuse players and GMs who will casually try to use things not available at the time, or assume can't use something that actually was available. No background materials will ever be detailed to prevent this.
The "Final Voyage of the Mary Celeste," for example, takes place on a sailing ship in 1872. Players have tried to include features the ship did not have, such as locking up unruly characters in a non-existent brig. In at least two runs players have tried to make ship sail around in little circles by trying the wheel over in a turn. Sailing ships will not do that, they turn into the wind then stall.
In the "Mary Celeste" there should be two modern (for the time) revolvers in the ship's weapons locker and two antique muskets in one of the character's private sea chest. During one run we were unable to separate the props into different chests and just had them all in the same bag behind the GMs table. When a player went to the weapons locker the GM, who didn't know a lot about guns, handed him the muskets.
Then there was a player who came into the game very late and had no briefing at all. He went up to a GM and pantomimed speaking into a microphone.
"I need to get the Captain on the intercom," he said.
"It's 1872," pointed out the GM.
"Oh, well, I assume there is some sort of intraship communication I can use."
"Um, well, since you are all on the same deck together you can just walk over and talk to the Captain." The GM points. "He's right there."
Games that take place in the present do not have this problem. However, it is amazing how fast games go out of date. When I first wrote "The Marin County New Age Society Cocktail Party" it was meant to be a locked-box murder mystery with the characters cut off and unable to communicate with the outside world. Now imagine ten characters, all California stereotypes, and not one of them has a cell phone. This was plausible when the game was written in 1991, but today? Not a chance!
Last year I revised the 12-year old "Uberman's Wake" game for a new run. Some changes were easy to make. Mayor of New York David Dinkins became Rudolf Giuliani. References to President George Bush didn't have to be changed at all. Some temporal effects were more troubling. The characters had gotten old. The extra 12 years made a big difference to characters who had seen action in World War II. A couple who were Vietnam veterans were now raising a 13-year old daughter while pushing 60 themselves. And a Nicaraguan character was no longer the young woman in her twenties described in her character sheet, not if she'd been a teenager when Samoza was in power.