Curious if anyone else has seen this happening for them as well the last little while.
The last few weeks every time I have recieved any blueprint they have been for the Tier 3-6 Polish and Czech tanks even tho I have a bunch of higher tier tanks that still can use fragements on lines I have actually been working on or abandoned. Have recieved enough fragements for 100% off on the LT vz.38, ST vz. 39, Skoda T 24, and DS PZInz all from 0%, then 2 for the S35 CA, 5 for the 25TP and 2 for the Skoda T 25.
Nothing for anything that isn't the next tank in the line from where i am up to unless I am at 100% on all the ones before. So it seems like the list that they are using is that they take all the ones that you have 100% discount or completed the research and make a pool of the tanks that come next to pull from. Kind of nice if that is the case as it means I don't have to worry about getting all the Tier 8+French vehicles for example long before I ever get too them.
Source: https://www.reddit.com/r/WorldofTanks/comments/rvo9mj/blueprint_system_changed/