Is there a format that I could/should be using to determine the UTC date-time string of any historical UNIXTIME value?

I'm thinking something like $asctime($calc(%unixtime - $timezone + $daylight)) but I can't seem to get the logic right to work in both Summer and in Winter.

I would also like to report a pseudo-bug in $asctime() in that it will not support negative UNIXTIME values. (although $gmt(n) does support negative unixtime values). ((why would I want $asctime to support negative values? so I can adjust for $timezone when passing 0 (zero) epoch time, and get Jan 1 1970 result. And so I can get results for somebody's birthday if they're born prior to epoch. ie, if they just turned 65, I can subtract 60*60*24*365.25*65 from $ctime and get the day of week they were born on)).

Well. At least I won lunch.
Good philosophy, see good in bad, I like!