Thank you for this method to reset the ID counter to 1. Although inelegant, it is at least one way to accomplish the result. If anyone knows a less dramatic way to do the same thing (without disabling slideshows on the site for a short while), let me know.
Regarding testing... in theory you are correct. In practice, not so. Testing on the local machine produces a different result (particularly for slideshow titles) compared to publishing on the actual site. Presumably this difference is due to more/different CSS content in play. But regardless of the reason, a significant difference exists. It's not a problem, however, provided there is a way to reset the ID counter. Which there is.