Neville first meets Louise and advises her to go to Paris
Date (happened)
between 1945 and 1950
unresolved
between 1945 and 1950
estimated · possible · preferred
Reasoning
'20 odd years ago' is a rounded colloquial figure taken as roughly 20 to 25 years before the telling, not an exact count. The telling itself is dated to after 10 November 1970 by internal evidence in this same lecture (possible confidence, since the catalogue-only 1970 claim cannot be relied on alone), so the meeting is estimated between 1945 and 1950. Capped at possible by that weaker input.
Told / reported
between 10 November 1970 and 31 December 1970
estimated · possible
Reasoning
Neville tells this story in this same lecture; the telling date is capped at the lecture's own possible-confidence delivery bound.