Nobel acceptance speeches cannot be "off the cuff," as the winners must submit their speeches 24 hours in advance so they can be translated into Swedish.
Nobel Prizes are awarded in December.
When Sheldon and Leonard reassemble the DNA model, Sheldon gets the atom colors wrong. He says carbon for a white ball (hydrogen) and hydrogen for a red ball (oxygen).
Sheldon's mother Mary does not appear in this episode despite the fact that he has won the Nobel Prize. Mary has appeared in multiple episodes, including the season 8 episode, The Maternal Combustion (2015). In that episode, Sheldon states that his mother has been present for every award he's ever won. It is out of character for her to miss seeing him accept the most important award he's ever won.