|Unit Name||Year||2nd Year||Offset|
|SP Rct Artillery||1940||1940||2|
|Super Heavy Armor||1943||1944||3|
Police and Engineers are a special case, as they have a 2nd fixed year. Thus they have a tech in '39, and the next in '42, before the offset starts.
And offset of 2 years, means that, in the case of Militia, they will be level 1 with 1918 techs, 2 with '34 techs, 3 with '36 techs and so on, with 2 years for each new tech. They would then be level 7 in 1944. Here's also the reason why Airborne is starting at level 3. Because the techs they use, starts in '18, level 1, but the techs you need to have researched to be able to make them, are level '38 techs, so you'll have to research '18, '36 and '38 techs to get them, which is 3 levels.. Also goes for Marines, but they don't need the '38 techs, thus level 2 on them.
So, now you'll be able to figure out what you'll want to use for different pictures for different levels of the brigades, as you'll be able to figure out wich year the different levels are. For tanks, and planes and ships, you should look into more than just years. Here's a rough overview of the most common:
Infantry, Mountain, Marines and Airborne:
Level 1 - 1918
Level 2 - 1936
Level 3 - 1938
Level 4 - 1940
Level 5 - 1942
Level 6 - 1944
Level 7 - 1946
Level 8 - 1948
As far as I know, you'll have to make the pictures say 0 for level 1, and 1 for level 2, and so on... Basically, a number to low.
That's it, hope you found it useful!