Naming/Numbering Convention for Matches

I've been tasked with a statistics project where I can analyze any data I'm interested in. So, I chose League of course! :D

I obtained what I thought was a random sample of a recent patch from the API (https://developer.riotgames.com) when I ran into a problem. I was operating under the assumption that all match Ids that were possible existed. For example if 1777414575 is a match ID and 1777429574 is a match ID then all integers between them will also represent matches. I recently noticed that this wasn't the case and I have no idea what my population size is anymore (the number of total matches played in the patch).

Does anyone know or remember reading anything about how Riot decided to number matches, or can direct me to a related forum? If so, I'd really appreciate all the information I can get.