The "solution" in this thread seems to be just an acceptance that some players and TV's display things incorrectly, but I think there is a more solid answer (though the fact that players/tv's display according to their respective settings is certainly true).
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The solution for me was to go to those videos, right click on the video asset (not the timeline, but the actual video), "revert to original," and then "select transcode settings." From here I could set the transcode setting as 16x9 HQ DVD instead of "automatic" so that the final video output was widescreen instead of the 4:3 that was getting stretched (Encore wants to leave a 4:3 original video as 4:3, which might make sense, but is not what we want for a 16:9 DVD!).
No real argument with any of that, except that you are dealing with a different problem - keeping 4:3 source as 16:9.