naggindragon said:
I like the think of the Butterfly Effect (not the movie, the effect). Sam singing this song might not seem like much at the time, but it could make profound changes to the future. It's sure to stick in Katie's mind... so when she hears the song for real surely she must put 2 and 2 together...
So I think Sam would have succeeded in changing his sister's life for the better.
Except, it's when she's crying, after Sam's sung "Imagine", that Al checks the handlink and tells Sam that nothing's changed - she still marries Chuck. If hearing Sam sing Imagine in "1969" had an effect on her future, then when Al checked the handlink, that information would have been there since it seems that Al's able to impart information on changes in history pretty much immediately after the action that would cause the change.
If there was anything that would have a possible impact on Katie's future it would most likely be Tom not being killed in Vietnam but even that's doubtful. A graduate of the US Naval Academy must serve a minimum of 5 years after their commissioning. It seems that it hasn't been that long since Tom's commissioning in "The Leap Home".
For arguments sake, let's say that Tom was commissioned in early 1969. That means his obligation to the Navy would run through 1974. It's in the episode "Promised Land" the elderly couple does say that he's just gotten back from Vietnam but that would be in keeping with historical fact. His tour in 'Nam began in either late '69 or early '70 and a tour of duty in Vietnam was the period of a year. So when they talk of him coming home, it could be in the sense that he'd returned home from Vietnam and has been granted leave. The timing would actually worked out well if he'd been sent to Vietnam in late '69 and then at the end of his first tour re-upped for a second tour. The date of "Promised Land" would be about the time frame that second tour would have ended.
He still, however, has about 3 years left in his obligation to the Navy. He also could have chosen to remain in the Navy when the five year period was up and, if that were the case, he wouldn't have had much more impact or presence in Katie's life than Sam did away at school.
Personally, I don't think there was any change in Katie's life just as there was, most probably, no change in John Beckett's life. Some things are just meant to be and this may be one of those cases.