Why didn't Tuvok tell Janeway that R'Mor would die before giving him the messages?

Question

In the episode Eye of the Needle, they come across a Romulan named R'Mor, who they transport to Voyager from 20 years in the past.

Before sending him back in time, they give him messages from the crew that he promises to give to Starfleet in 20 years. After transporting him back, Tuvok tells Janeway that R'Mor would die 4 years before he's able to send the messages.

Why did Tuvok wait until after R'Mor was transported back to tell Janeway he won't be able to send the message, why not tell her before she gives him the messages?

Answer 1

The Temporal Prime Directive specifically forbids actions that might interfere with the normal course of events.

Tuvok's discovery of Dr. R'mor's death-date would have a radical effect on the timeline if was inadvertently leaked to him. It would appear that Tuvok simply didn't want to take that chance that someone (perhaps even Janeway) might be tempted to help R'mor not die in order to make sure their messages had a greater chance of making it to Starfleet

TUVOK: Captain, I did not want to mention this until after our guest had left. I checked the computers databanks for a Romulan scientist named Telek R'Mor.

Note the extreme emotional response from Janeway, Torres and Kim when they hear the news. They look heartbroken and would clearly have been prone to trying to 'do something' to fix the situation.