The reason for the different I Love Lucy openings was simple- syndication.
The one that most of us are familiar with- the two hearts on a simple background- was for syndication, as the original with the "stick figures" was rife with references to the show's sponsor at the time, Philip Morris (and as time progressed, subsequent sponsors), making it unsuitable for the rerun market.
When you figure all the subsequent sponsors, there were probably quite a few original openings/closings, hence the generic versions thst we're all familiar with.
Learned this on TVLand- when they ran the show, they made a big deal about restoring the original credits and explained the whole situation.