What was this used for? (Newbie question)

Hey guys. I just bought a 2016 ORSB Tacoma last month, and I can't stop reading things to do to it on TW. Thank you all for the great ideas and info.
I have a newbie question about a modification that was made to my truck prior to me.There are cuts to the bedrail caps and holes tapped that aren't equidistant from each other. There are also a couple of tapped holes near the back window as well. Pictures attached.
My questions are what do you think was mounted here and what else could I possible mount using them? Thank you for any input!

 

I believe those are for the OEM bed cover that comes from the factory. Don't quote me on that... unless I am right. HAHA

 

That’s interesting. Those holes look factory. It almost looks like a bed cover or rack of some but why they didn’t just use the track right below beats me.

 

Potential mounting points for things like hi lift jacks, gas tanks, or some bed molle system

 

I'm not 100% certain but maybe a bed rack?

 

Thank you everybody! It does appear that it was for an OEM bed cover. Apparently every tacoma comes with these predrilled holes, you just cut the bedrail caps to expose them. Thanks for pointing me in the right direction.