Ahhh so say a 3640 is the 3600 series with 40 compartments? If that is the case then how do you know how many are in the 3700?
So right there's where this train went off the tracks... You're applying logic to something that's not logical!
The 3700, 3600 and 3500 series identify an overall form factor that matches tackle bag size and you will see THAT consistency across multiple manufacturers. Initially, some of them probably did make logical sense on the last 2 digits but then a new one didn't fit the logic or conflicted with something else. Think about it, say two "3740"s (by logic: a 3700 family - 40 compartment box) but with different layouts or different depths. End result: last two digits just became a model number.
Bottom line is that some of them WILL make sense. Most won't. I end up just looking them up.