Thanks Hirohito888. I ended up doing the online checkin at ANA's website. What threw me off initially was the fact that I could NOT view my reservation on ANA's website, after providing a valid ANA confirmation number. I even tried the ticket number option. I guess it had something to do with the way the booking was made - I did on united.com.
Even though I could not view my reservation, I found out I was able to check in
. So all was well, and I got to know the various TG lounges really well...
Cheers
@ORD