Archaic mechanics in Maple.

if the expiration date is the same for all, stacking isnt a problem, but, when item creation determines individual expire times, how can the game, or even the player tell when the first created item expires, compared to the last created item?

Mabinogi averages the expiration date.

Item A expires in 10 days, Item B expires in 20 days. Together expires in 15 days.

Stack of 2 expires in 15 days, add another 10 day expiration to it. Gets 13.3 days remaining.