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If it's deliberate flagrant copying of your content I also tell them if they don't inform you shortly that the data has been removed you'll contact their hosting company and inform them of the copyright infringement (all hosting companys are bound by law to not let this happen). This usually gets a quick response.
If you have any of this data posted on a site with your permission (hopefully dated) this will help prove who had the content first. Linking to Google's Cache of your site or the offenders site may also help.
There is a site on the net where you can verify the original date of the content but I forgot where that is.
I do this all the time for my clients. I've had one prolific content thief have several of his websites removed for doing this. Responsible site owners and hosts usually respond within 24 hours.
PS. I use "no archive" in my robots text so search engines won't freely copy my content so you may consider that for future reference. It won't stop prolific thiefs however.
<META NAME="ROBOTS" CONTENT="NOARCHIVE">
You have a lot of pages so it's going to be a big job.