Alert when multidimensional timeserie do not include data in past two weeks

I would like to ensure that a value with specific tags exists at least during the last two-week period. I ended up giving up on doing this in one InfluxQL query. However, I found that it would be possible(in theory) by doing two separate queries in an alert, taking the last element of the last two-week (time series A) and last one-month (time series B) periods. In theory, both of those should have the same values if we assume to get measurement reports daily. But elements that are common in two time series can be handled in a math operator; there is no possibility to take elements which are not in both. Is that kind of “set difference” possible to compare in alerts, or do we have another solution to alert if value has not seen in last two weeks?