Gave it a try, to see if there was any issue. First time didn't see the convoy and checked with the editor, thing was I went too far east and never intersected.
At second try I put north route, keeping west side of meridian 31º (tip was on the briefing, british boat is east of that line and it's not supposed to cross it unless in hot pursuit, so it stands to reason that you are supposed to do the same in your side). And catched the convoy with 22 hours remaining.
I went north straight, creep speed, shallow depth. Nothing weird nor gamey, so it can very much be done.
Still you have a point in that when the "spotted at 64N 34W" event triggers, the convoy it's at 65N 34W. Errata, or fog of war, only Mister Gellis knows.
< Message edited by Ancalagon451 -- 1/17/2019 3:46:41 PM >