[jeffschevelle]

Here is some info regarding the likely reason that "Best Way To" disappeared from all AC filters by at least mid 1975 -

AI's summary: "In the 1970s, the Federal Trade Commission (FTC) aggressively tackled unsubstantiated claims like "the best" by requiring advertisers to possess a "reasonable basis" (actual evidence) for superiority claims before running ads or issuing marketing materials or slogans, thus requiring a move away from subjective, vague marketing to evidence-based advertising. The commission targeted deceptive advertising, initiating actions against companies making unsubstantiated claims."

I never trust AI. But above is confirmed by this blurb from the published 1971 FTC Annual Report: "Perhaps the most significant action of the year was the adoption of the Advertising Substantiation Program. Under this program, the Commission announced plans to select numerous important industries each year, and to require major advertisers in those industries to submit whatever documentation they have to substantiate those aspects of their advertising which constitute measurable claims of safety, performance, efficacy, quality, and comparative price. To implement this program immediately, the staff prepared Orders to File Special Reports for issuance to domestic and foreign automobile manufacturers, with the response to those reports (aside from trade secrets) available to the public. Thus, for the first time, the consumer will be able to evaluate the support for some of the advertising claims of major companies."

I suspect it was very difficult, if not impossible, to produce any evidence to substantiate that, out of ALL the filters on the market, an AC filter was THE BEST way to protect your engine. So it was likely easier to just remove BEST WAY TO from the filters than to fight with the FTC about it.