How does Longstreet know about Herdeg?

First off, the original Philadelphia Experiment only worked because Longstreet was running experiments in both 1943 and 1984 and linked those two years together. Once the experiment ended, the 1943 Longstreet should have known nothing about what happened except that Herdeg was no longer on the Eldridge, which shouldn't seem so odd considering what happened to the rest of the crew. He shouldn't have known that the disappearance of the Eldridge was caused by time travel nor that Herdeg would end up in the future.

Furthermore, once Mailer's 1993 experiment sends the Phoenix back and alters history, there will be a new timeline. In the new timeline Longstreet never conducts the 1984 experiment so 1984 never connects to 1943 so the original Philadelphia Experiment should have had no effect, and Herdeg should have remained in 1943 in the new timeline. I can accept the Herdeg from the first film shunting over to the alternate 1993 but there should also be an older Herdeg who always remained in 1943. Therefore neither Longstreet nor Mailer in 1993 should have any knowledge of Herdeg.

To take that a step further, if Longstreet's original 1943 experiement had no effect then he probably would have abandoned the project, and the 1993 Mailer would have had nothing to base his experiments on, so there should be no working time machine. The story would have made more sense if Herdeg had to convince Longstreet to dust off 50 year old research because it actually worked and Longstreet had no idea. Instead we get Herdeg who doesn't seem to understand anything even though he actually lived it, and Longstreet who has all the answers even though he lived through a timeline where none of it happened.