Hi Kenyon,
Thank you for posting your concern.
On the AdWords API perspective, you may only retrieve targeting ideas using the TargetingIdeaService. However, according to this guide, it's currently not supported to specify the date ranges when using the said service. You may also refer to this guide for more details.
With regard to downloading report for Historical Metric information for the keyword planner, unfortunately, it is currently not supported in AdWords API reports. The only available historical fields for keywords are:
Otherwise, if what you are using is the Google Ads API instead of AdWords API. Please let me know.
Regards,
Hiroyuki
Google Ads API Team