Not necessary, because even if fewer than most viewers who tune into the first episode will do so because of the ad, the ad can still be less likely to attract viewers who are likely to continue watch as the other ad would have attracted.

Necessary, because if it were not true — if the advertisement that the program’s producers favored WOULD have grossly misrepresented what the program would be like — then we have no reason to think the ad favored by the program’s producers would be different from the TV network’s ad in terms of its potential to give viewers false expectations.

Not necessary, because the conclusion concerns a claim about the relative potential of the two ads to attract viewers who are likely to continue watching. The author believes the TV network’s ad isn’t as good at attracting those viewers as the other ad would have been. But this comparison doesn’t require any belief about over half (”most”) of viewers and whether those viewers were attracted by the ad or not. One ad can be worse at attracting long-term viewers than another ad regardless of what proportion of viewers tune into the first episode because of an ad.

Not necessary, because “almost all” is too extreme. The conclusion is just that the TV network’s ad won’t be as good at attracting long-term viewers as the other ad would have been. This doesn’t imply the author thinks that “almost all” would have continued watching had we used the other ad. The author just needs to believe that MORE viewers would become long-term viewers had we used the other ad.

Not necessary, because the conclusion concerns a claim about the relative potential of the two ads to attract viewers who are likely to continue watching. The author believes the TV network’s ad isn’t as good at attracting those viewers as the other ad would have been. But this comparison doesn’t require any belief about over half (”most”) of viewers and whether those viewers missed the first episode. One ad can be worse at attracting long-term viewers than another ad regardless of what proportion of viewers watched the first episode.