is that future robot killer Zeitmann mailed the cards into the past so that they could be delivered as a warning not to Fist but to Zeitmann's younger self, warning him that today (that day, in the past) was the last day of his life, the day that Fist would strangle him with his own spine, which was ripped from him so quickly that he didn't even have time to die from it before it was used to strangle him, but Zeitmann didn't bother to address or explain the cards because he knew his younger self would recognize his own handwriting and piece everything together using his super smart brain thus making such contrivances unneccesary and in fact even dangerous if the cards should ever get waylaid in the mail as possibly they did since they were delivered to the wrong person, namely Fist, which you would guess was a coincidence but in actuality it wasn't because Fist was coincidentally living in Zeitmann's old British home that he used for vacations in Britain back when he was alive in the past and where his past self would have been if the letters were delivered at the proper time in the past, which they weren't, because let's face it, interchronogogical mail service is simply rubbish these days, I mean the amount they charge for stamps you'd think they could at least get the right decade, though I suppose in their defence there are an awful lot of decades to choose from and if you just write '89 on your letter that could be like a billion different '89s to choose from in an all-of-time sense but I digress because the point is that past Zeitmann never got the warning cards that his future self sent to him until a long time in the future when his future killer robot self went back to his old British apartment to see how it was and relive the old days and found the cards still sitting there like they had never been torn up and eaten to destroy the evidence, which he knew his younger self would do, and that told him that someone else had gotten the cards and could possibly deduce the whole plot, a plot that involves the US and Russian governments fighting a secret chrono-war at all points in the past and future using robots and quantum brains in which Fist was the rogue agent who could bring them both down if he ever found out, so future robot killer Zeitmann had no choice but to travel into the past and warn his younger self face to face but once again the time service had the same glitch and delivered him to his British home at the wrong time where Fist was waiting leading to the unfortunate situation in which Karen kills him and then she and Fist stay drunk and then deduce the chrono war time travel robot killer killer robot plot and put an end to it in the second part of the trilogy, The Even Laster Day Of Your Life, which sets up a cliffhanger ending in which Fist learns that he is his own father, while hanging from a cliff.

It was quite clever of you to include all of that in the subtext so that we could figure it out.