How do you prevent the appearence of ‘immortals’

I haven’t played Microscope yet, but I’ve watched various playthroughs and read the book multiple times. One thing I’m struggling to understand is the game’s stance on how period lenght should relate to the characters’ lifespan. The book says this:

“Another good rule of thumb is never to have character lives span more than one Period since that starts to weld adjacent Periods together.”

Which makes sense. Not only does this weld adjacent periods together, but also makes the two periods dependent on each-other and harder to wedge anything in between. If a character appears in multiple periods, she becomes immortal almost ‘by definition’ as from that point onwards it doesn’t matter how many new periods will be inserted between those initial two, the character would still be alive in both.

And there seems to be a natural tendency for the players to try to tie the history together, by putting the same character into different periods. I’ve seen it in multiple games, but no one called it out as a violation of the rules, or something that should not be done. If such thing happened, the players always commented along the lines of “Oh, so those two periods are that close together. Now we know that. Okay, let’s move on”.

I do understand that a group could put ‘Immortality’ (and ‘Time travel’) on the Palette, but for me that sounds like a waste of Palette space, and if someone has to explicitly add it to the Palette, this robs the player from adding something of her own. I also do understand that a group can make a house rule of not having these things in game even if they are not on the Palette. Or to add them to the Palette ‘by default’. It just seems weird for me that banning these is not among the rules. Not even as optional ones.

How do you manage this in your group? Is this really such a problem, or am I reading too much into it and Microscope is really entirely functional if characters’ life can span across multiple periods?