I have been experimenting with the API, and it seems to work well, except for one issue:
There doesn't seem to be a way to see past the 1000th result in a search query.
The "/search/companies" method allows you to set the items_per_page and start_index, but if you set the start_index to anything higher than 1000 it returns an error. The same error is returned, for example, if you set the items_per_page to 20 and start_index to 990, although it works OK if start_index is 980.
Therefore it seems that attempting to access further than 1000 search results results in an error.
Is this an intentional limitation?