I often hear sales teams say, "we want to clean up our REPS database before we implement new reports." While I can absolutely understand the desire not to spend money reporting bad data, seeing bad data can be a strong motivator for your sales team to use REPS the way you want them to.
When all their phone calls and meetings don't show up on the weekly activity reports, sales people often get cranky. "Hey! I made more calls than that! I deserve more credit!"
In many cases, their numbers are wrong because they aren't entering each activity into the database or they're entering it incorrectly.
Showing them weekly reports with bad data, and also sharing those reports with their bosses and company leaders will very quickly motivate them to start putting everything into the database. They'll want the credit for doing the job you've asked them to do.
The next time you consider holding off on reports so you can clean up your database first, think about how much easier it will be to get your team on board when their incorrect numbers are being sent around and talked about. No good sales person wants low performance numbers going around....they'll make sure to get their activities in the way you want.