Raj is wearing the ring before Tina puts it on his finger during the engagement.
In the opening sequence, the young Pooja is seen mouthing Raj and Tina's lines between her own lines.
The movie, set in 2002 shows that Raj and his family left India 10 years ago in 1992, a time when the World Wide Web was not available in India, but right away from that moment, Pooja promises Raj on contacting through e-mail and starts doing it right away.
When shopping, Raj tells Rohan that Pooja would never wear a particular color. Actually, she has worn that color (pale yellow) at least once in the movie, and possibly twice.