I don't remember ever hearing the Cream commercial for Falstaff back then. I only became aware of it about 5-7 years ago from a radio show that featured a bunch of pop and rock & roll singers and groups doing commercials from the 50s and 60s. There were some unexpected names for sure. Bill Haley reading a Civil Defense public service spot, Nat King Cole for Italian Swiss Colony Wine, and ads sung by everyone from the Blue Magoos to the Bobby Fuller Four. IIRC most or all of them were on a series of bootleg CDs.
You can find all sorts of 60s oddities on YT now.