Most large social media providers have set up "data liberation" procedures that you can use to retrieve your entire history, but they are typically hidden fairly deep in settings.

Facebook

See Accessing Your Information in Facebook Help.

1. Click  in the top right of Facebook.
2. Select Settings & Privacy > Settings.
3. In the left column, click Your Facebook Information.
4. Next to Download Your Information, click View.
5. To add or remove categories of data from your request, click the boxes on the right side of Facebook.
6. Select other options, including:
    * The format of your download request.
    * The quality of photos, videos and other media.
    * A specific date range of information. If you don't select a date range, you'll request all the information for the categories you've selected.
7. Click Create File to confirm the download request.

In step 6, select "JSON" for the format of your download request. You will receive a notification within 24 hours that your files are ready for download.

Twitter

See How to Download your Twitter Archive.

Go to your Account settings by clicking on the more  icon in the navigation bar, and selecting Settings and privacy from the menu.
Under the Account section, click Your Twitter data.
Enter your password under Download your Twitter data, then click Confirm.
Click the Request data button. If your Twitter account is connected to Periscope, you’ll have the option to Request data from Periscope as well.
When your download is ready, we'll send an email to your connected email account. From your settings, you can click the Download data button under the Download data section.
Once you receive the email, click the Download button while logged in to your Twitter account and download a .zip file of your Twitter archive. 

LinkedIn

See Downloading Your Account Data.

Click the  Me icon at the top of your LinkedIn homepage.
Select Settings & Privacy from the dropdown.
Click the Data Privacy on the left rail.
Under the How LinkedIn uses your data section, click Get a copy of your data.
Select the data that you’re looking for and Request archive.

Participating in the Alpha Test

Send email to fredzimmerman at gmail doht com.