I think your pretty brave to base a restart on the early RC's
Until now the only the most glaring bugs are fixed.
No improvement of overall strategy(RC4).
No functional improvement of the diplo AI so all the world joins the allies including all the neutrals (Sweden, Norway, Denmark, Finland, Netherlands, Belgium, Switzerland, Ireland should all stay neutral in an average game if not attacked) RC4.
The production AI has been slightly adjusted (unknown effect, RC4).
Japan/China is totally unbalanced (now just the other way, RC4).
I gonna check if USSR still leaves Leningrad open in case of winter war, this happened in the 3 last games of 1.3 (which wont happen in my current test game as Finland joined the allies) or in any other war.
USSR still insist that Murmansk is the best place to build new industry and that its a good idea to convert the entire Kola peninsula into a giant industrial park (on VH at least, RC4).
Tactical AI thinks the word retreat is a town in Russia (RC4).
AI still mills apparently senseless around even in front of openings in the enemy front.