I've only done this once, and fortunately, the correct job was just across the street from the one I wrongly showed up at. Everyone got a big chuckle out of it, though.
I'm pretty meticulous with my calendar, and additionally, each year, when I book the jobs for the next 12 months, I mail them a "Confirmation of Appearance" letter listing all the dates and times, and also follow up with an annual contract they sign and return to me. My wife says I probably do too much paperwork along these lines, but I'm a nut case anyhow, so it helps retain my insanity.
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Good Luck,
Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)