If you are referring to the reports in the text box, and sometimes with a box and a tail on the NavMap (if your mod mix does that), then each Random Generated Group in the RND file, and each Group or Unit in the SCR file can have a time and percentage "set" for a broadcast notification of the group's/unit's existence after it "spawns" into SH3. Sort of like a "spy" is watching the harbor, or an airplane saw it, maybe another Uboat saw it. It does help with "atmosphere", making a person playing feel like they are part of the imaginary SH3 world. Depending upon when that "message" is set to trigger, it might be "fresh" data, and it might be quite "stale", or old. When it gives a direction of travel, that is an approximation of the direction of travel at the time of the report. If the group does a turn right after the report, oh well, you'll be off a good little bit if you're looking for it. Generally speaking, if it's not close, leave it be, else you'll waste a good bit of fuel, and crew patience (and the skipper's)... If instead you are looking for the convoys near a harbor, as blackswan40 mentions, they may well reach their "termination" point and literally disappear. Also, if you are in too close to where a group is supposed to spawn, it won't spawn, because you're in too close...
(thank you, Mr. Obvious) One thing you can do with those reports is to "track" them, and by that, you are able to draw the "shipping traffic lanes"
