At about level 30 my smithing skill was around 75 and I used a smithing potion to create a glass sword with a base damage of 42 and an improved damage of 72. At level 42 with a smithing skill of 100 with or without a potion the glass sword I created is only 38 and the improved damage is 62. What gives, am I missing something or is this a bug?

maybe you wear a different ammount of fortify one-handed/two-handed in your equipment.

the potions only increase the upgrade not the base.