I disassembled and assembled back SM-T805 for motherboard replacement 2 hours ago. Discovered that back cover have a row of tiny pins with tips molded into back cover rim who are designed to break out and larger pins who will click open and back on closing just fine. Also back cover rim is glued to cover with weak glue. Seems someone Samsung decided that those larger pins alone are not enough to keep back cover firmly in place without flapping around. In reality larger pins alone on assembling will click back and keep cover in place just fine.
However I agree to you that correct way is to carefully open this tablet from screen side with these small blue flat openers or with plastic cards. It will be faster as well. Back cover rim should be removed only to replace antennas. I hope that author of these manuals will fix that.