What are the differences between Apple Thunderbolt Displays during their production years from 2011 to 2016?
Only two "models" have been produced:


MC914LL/A (July 2011 - ~July 2012)
MC914LL/B (July 2012 - June 2016)


The only difference between the two models is an additional MagSafe to MagSafe 2 converter which was shipped with the latter model. It allows to charge MagSafe 2-equipped Mac computer. The actual displays are the same.