Hello MNRoth,
I can't tell from your question if you are working with a Mac or a PC, and what application you used to transfer your photos. I've included a resource below that will explain how to import your photos from the iPhone onto your computer. Hopefully this method will pick up the 20 that are missing.
If you have My Photo Stream enabled, and the images were taken with the iPhone, that would be another way to get them on your computer.
Import photos and videos from your iPhone, iPad, or iPod touch to your Mac or Windows PC - Apple Support
https://support.apple.com/en-us/HT201302
Archive or make copies of your iCloud data - Apple Support
https://support.apple.com/en-is/HT204055
You might already have a copy of your library in iCloud Photo Library beta and the last 30 days of photos in My Photo Stream:
- If you enabled iCloud Photo Library in iOS 8.1 or later, your photos and videos are automatically uploaded to iCloud at full resolution. You can download the original photos and videos from iCloud.com, or select Download and Keep Originals on your iOS device, then import the photos to your computer.
- In OS X, My Photo Stream photos are automatically imported to your iPhoto or Aperture library, unless My Photo Stream and Automatic Import are turned off in iPhoto or Aperture preferences.
- In Windows, My Photo Stream photos are automatically imported when My Photo Stream is turned on in iCloud for Windows (or iCloud Control Panel).
You can also use the steps below to manually copy your photos and videos. Any comments or likes attached to a shared photo aren't saved, and photos and videos saved from shared albums aren't full resolution.
Regards,
- Judy