The upgrade path I take from a factory reset of my Aura2v1 is: 4.*.***** > 4.7.10075 > 4.12.1211 > 4.18.13737.
About the digit vs character, my thinking was based on how I was parsing it in my tools (and that a character is an int). I'll update the note soon.
In addition, it isn't the end of the world (at least so far) if you update with the wrong hardware zip, as long as it isn't between too many versions. All that will happen is the kernel and uboot won't be updated, which may mean you miss out on a bugfix or two or that the soft reset acts funny. I regularly do this when testing the recent mark7-only versions. I wouldn't recommend it though, so just upgrade randomly.
And yes, the wiki is quite out of date. Most people seem to go to my site anyways, as I recently overtook the wiki page consistently in Google, and the unique pageviews per week have been increasing rapidly since the first week of September. Based on normalized numbers from
https://kfwproxy.geek1011.net/stats (hits+misses)/85/(for÷(24×7)) and my logs (to get rid of bots and account for the increase and people refreshing constantly), I'm currently at just under 8.5K views per week, with an average of 5K/week over the last month and a half.