upgrade a slide is normal also after few years. You make a new presentation in a new place, change the first with the new data and the old pages with news.
The problem is that when you upgrade a slide in slideshare you loose everything.
Why?
A possible feature is the possibility to have a slide history e.g. version 1.0, 1.1, ..., 2.0 ...
I hope this is for you a good a idea.
For me it will be a great feature ;)