Why does only one of my routes get sent to my GPS?

When I send several routes to my GPS, only the last one shows up. What's wrong?

If you have a Magellan GPS receiver, or an older Garmin receiver like the GPS 12, your GPS uses numbers to identify routes. Each route must have a unique number, or else it will overwrite the other route with that number. Edit your routes, and give each one a unique number.