Looks like you got most of the info
05E is build date 05=May & E=fifth week
PO16891-Built at Pontiac (PO), MI plant--the rest is the body number
Accessories- check if the car has this stuff 1E-tinted glass, all 2P-radio 2V-Vibrasonic/Reverb 5Z-seat belt delete. The tags did NOT list all the options on the car. Not too sure about the 2V code.
1-16-Don't know, some type of internal tracking? My 64 GTO was built 06C-third week of June-and has 2-14 in the lower right corner.
Numbers are the serial number