The formulas only produced approximations, and then rounded to 5-second boundaries because the tz data format didn't have enough bits.
[ISAAC J SCHWABACHER firstname.lastname@example.org]
Little known fact: if you have a sub-minute-resolution UTC offset when a leap second hits, it rips open a hole in the space-time continuum and you find yourself in New Netherlands.
Tell me about it! Last time that happened I had to grow stinking tulips for 3 years to get enough money to sail back home. I'll never use a sub-minute-resolution UTC offset again ;-)