The Access Narita website mentions a baggage limit of one 20kg bag per person. I wasn't aware of the limit when I took the bus last month from NRT to Tokyo Station. The driver, who also loaded the luggage, did not mention the limit and accepted my bags.

A few days later, going from Tokyo Station to NRT, the attendant who was loading the luggage was enforcing the limit. He suggested that I take the other bus.

I went around the corner and over a couple of blocks, and luckily the Tokyo Shuttle had just pulled up. I asked the attendant if there was any problem with more than one bag per person, and she said it was fine. She even tagged the bags and gave us claim tickets, which wasn't the case on The Access Narita on the inbound ride.

Interestingly, I later found that the Keisei Tokyo Shuttle Japanese language site also mentions a one bag limit.