When ejaculation is stopped deliberately, since prostatic and seminal fluid can backflow to the bladder, can it flow back into the ejaculatory duct?

Gotta go somewhere: This is a plumbing issue. If there is high pressure liquid coming down the pipe, and somebody suddenly blocks the end of the pipe, the liquid has gotta go somewhere. If one asks "can it" go there or "can it" go here... well that depends on how high the pressure is and how much liquid there is. In life, many things are possible, includine such backflow. If worried, one should avoid doing this.