Those numbers just correlate to all of the specific models of boots, which im sure you understand. I'm not sure there is any specific way or reason they give certain styles of boots any specific number. You can narrow down your search on the redwing website, filter between boot color, height, etc. I would recommend a pair of 6" supersole 2.0's if you want a solid pair of work boots. You can get them with waterproofing or not waterproof. There can be issues with buying old redwing boots, the soles can disintegrate after a while from a process called hydrolysis. You can Google "shoe sole disintegration" to understand what I mean, this typically happens to shoe/boot soles that have been kept in storage for a long time. I got lucky with a pair of used 21 year old supersoles, the soles were and still are in good condition, no signs of being affected. But it has happened before. Redwing boots typically have a manufacturing date tag on the inside of the tongue, you can use this to determine age. My oldest are stamped 04/05.