scanning photos, adding dates and losing them when exporting

I'm digitizing all my old photo albums by scanning them in. I put the photos into iPhoto and "adjust the date". Sounds great until I need to send them to shutterfly. Since shutterfly does NOT have the apple extension like they used to, I have to export them to a folder on my desk top before uploading. SO after all the work of changing the dates in iPhoto they get to shutterfly with the wrong date. Anyone know how to fix this? Thanks