I'm sorry I expressed myself a bit poorly. I don't mean to say we don't know how to read the numbers. I mean we might be reading as a literal numeral something that was meant to be read in a slightly or completely different way.
There's always the possibility that it is just some mythology without deeper meaning, that it represents garbled memories from pre-literary times. It might be encoding something we don't understand or just collectively misremembered stories or even just gibberish that came to be seen as significant purely by tradition or repetition.
We don't really know all that much about these peoples who lived at the early stages of our current post glacial stage of human society. We have a lot of data, to be sure, but very little in the way of a coherent interpretation for it all. In fact, the vast majority of the cuneiform tablets that have been digged up haven't even been examined properly yet, as in transcribed, translated and analyzed.
We have a few glimpses of the culture of Sumerian and some of it is this odd lists of names and numbers. I mean, even calling them "kings" is anachronistically projecting a very recent concept of Medieval Europe into a past at least 3 times as distant from as as the very earliest tribal leaders that came to be termed 'kings'. One common title used translated as 'king' (I am not sure it is written in these name lists) is lu-gal. It means 'big man', or magnate.
Hell, Sumerian is a language isolate. We interpret it largely based on context from later vocabulary borrowed by Semitic languages such as Akkadian and more recent descendants in Assyrian, Aramaic, Hebrew, Arabic and so on... Studying ancient Sumer and ancient Egypt is very very close to studying alien societies. We share very little with them other then happening to inhabit the same planet. We only understand Egyptian writing because some stone inscription had the same text in common late antiquity Greek, and ancient Egyptian written in hieroglyphics, and a script believed to be its more 'cursive' form.