I'm the OP. As it turns out, in the U.S. the complainant can use mail or fax as an alternative to G's online form. That information is not easy to find at the G site, perhaps because G prefers the latter method. And G indicates that using its online form helps expedite the processing of requests.
I plan to submit my requests by mail. I'll have a paper document to show exactly what I submitted and when -- just in case G fails to comply.