I think what they're saying is that 17-21 days after is valid, after 21 is not "valid" but acceptable. So for example someone receiving a 2nd dose on day 23 wou

I think what they're saying is that 17-21 days after is valid, after 21 is not "valid" but acceptable. So for example someone receiving a 2nd dose on day 23 wouldn't be counted to as part of a clinical trial but is not forbidden and no need for 3rd dose?