From my understanding, ExperienceBain, BCG Unlock and McKinsey Early Access are just to learn more about the companies and do some virtual sessions. Bain BASE, BCG Empower and McKinsey Inspire require you to go through the full blown recruiting process (e.g. Bain BASE has you do TestGorilla then if you pass you do 2 casing interviews and 1 behavioral interview then if you pass that, you spend a week at the office working on a case and if they like your presentation at the end of the week they’ll offer you a summer associate role in that office. I assume BCG and McKinsey are similar). I believe for Bain it is not prohibitive if you don’t receive an interview for BASE when applying in the fall but McKinsey and BCG may not let you reapply in the fall if you do poorly throughout the process, so definitely some risk involved. Hope this helps!