How can I know the acquisition date of this DigitalGlobe's Basemap

[Elijah]

I have been using this basemap -DigitalGlobe's 2m Digital Surface Model, HumanLandcape, and Basemap +Vivid; Nigeria-(http://www.arcgis.com/home/item.html?id=b9290a472e8e4d21aea3a9b826e52eee), and I have checked the metadata but don't seem to see the acquisition date. Is there anyway I can know the date of acquisition? I saw that it was created in 2015. What could be the acquisition date?

Thanks in advance.