Cancel my question, the million monkeys and Google finally sorted it. If you’re interested:
Line 1: titles
Lines 2 and lower:
Column A: flight date
Column B: flight duration
Column C: Date 2 years ago (Col A minus 730)
Column D: {=INDEX($A$2:$A2,MATCH(TRUE,$A$2:$A2>C2,0))} [enter the formula less the outer squirly brackets them press Control, Shift and Enter to enter it; the squirly brackets will return] [it’s an array, whatever that is]
Column E: =SUM(INDIRECT(CELL("address",INDEX(A$2
2,MATCH(D2,A$2:A2,0) ,2))):B2) except when I post that, an emoji appears in place of "colon D" so change it back.
Then copy that line down as many lines as you need and enter your own flight details in columns A and B in date order.
It won’t operate until you’ve entered at least 2 years data, and then only for the flights from 2 years after the first flight
But it works
Thank you and good night!