Last thing I can think of is
here. It's a post by Tegus, part of the Dev team, regarding a shield issue on steam versions. Hopefully that helps.
Each province has it's own tech level (from 0.0-5.0) for each tech. There are 8 techs per category, 3 categories. Levels only effect something at full levels, the .1 is progresses if you will.
What the individual techs do is different, Legalism allows your demesne to be larger, Bows improves archer attacks, they can decrease negative modifiers to relations from religion, culture, boost prestige growth, allow different buildings, increase siege times, increase taxes, etc, etc.
If the techs are applicable then province A would have more taxes than province B, ceterius paribus. If on the other hand A has extra taxes from churches, but has no churches, well then it doesn't matter.
What you might want to do is open the tech panel in game, and mouse over each tech, the individual stars. It tells you what that level adds, which might help you now what you want to focus on. For instance the English, might want to focus on Bows, since the get extra and better bowmen. Spanish and French might go for Cavalry weapons, since they get extra cavalry, light and heavy respectively. Heavy Cavalry already hits like a truck, might as well make that even stronger.
Often Siege weapons is a good choice, since sieges take forever.
Just remember, tech improvement is not fast, but if you work to improve it, and know how to, you can get a significant edge.