Hope this info helps you:
The difference in size is probably due to snapshots, the information is definitely there and might be salvaged but this requires tools and knowledge of the internal structure of .hdd files. One important file that you need to salvage is DiskDescriptor.xml, this file actually has the information about the real .hds names and their sizes along with snapshots. Each .hds file is a snapshot and one of them, probably the biggest one is the original disk pre-snapshots (last time snapshots where merged).
You can change the extension from .hds to .hdd and mount the disks to retrieve files using Parallels Mounter.app, right click on the .hdd file and choose to open with Parallels Mounter.app (it will fail if the file has the .hds extension).
If this doesn't work and if the data is important you should contact a professional data rescue service some of these services know how to handle virtual disks.
Don't waste money on data recovery software you find on this thread, these are spam bots posting ad spam, what you need is to reconstruct the hdd file and none of this software can help you with that.
Last edited: Aug 16, 2014