This episode features appearances of several (regular) guest actors who all played Raj' girlfriends: Kate Micucci as Lucy (last seen 78 episodes ago in The Itchy Brain Simulation (2013)); Laura Spencer as Emily Sweeney (last seen 20 episodes ago in The Application Deterioration (2016)); Alessandra Torresani as Claire (last seen 16 episodes ago in The Fermentation Bifurcation (2016)); and Katie Leclerc, who made one previous appearance as Deaf Emily in The Wiggly Finger Catalyst (2011). This is also the last appearance of all four characters in the series.
Raj mentions that he broke up with the woman he was dating. This is presumably Isabella from The Brain Bowl Incubation (2016).
Howard attends Raj's meeting with his exes to translate Emily's sign language. Raj had actually learned how to use sign language for Emily by the end of The Wiggly Finger Catalyst (2011), but he has apparently forgotten since then; and Emily has learned how to read lips in the meanwhile, because Howard no longer has to sign everything to her like he had to do in The Wiggly Finger Catalyst.
The fact that Leonard is looking for a new purpose for Sheldon's former room indicates that Theodore (Christopher Lloyd) from The Property Division Collision (2016) has moved out. This makes sense, since Theodore was established as being a day-to-day rental sublease for the remainder of the time that Sheldon had paid rent for, Sheldon's paid time should have run out by now.