I love Skyrim. I know a ton about it. I've been playing 8hrs a day since it came out. I have a job that requires only a couple hours a day so I have tons and tons of time for my hobbies. My point being I've been everywhere and done so many different things I lost count on day 1. With all my knowledge I still have some questions, some very dumb questions but I can't find a straight forward answer so please help if you know.

Okay then.
When you upgrade your armor or weapons the item will light up if the upgrade is available, also if you have the right item in your inventory to do the upgrade(iron/leather whatever it is your upgrading). Well I don't usually carry these things around so even if there is an upgrade I may not realize because it doesn't light up without the item needed to do the upgrade. My question is what determines this? How can I tell when I have an upgrade available without the neccesary item.
Example. I had smithed up some dragon armor. I had some scales leftover and nothing highlighted for an upgrade. After doing some quests I went back and the upgrade was available. Why all of a sudden when it wasn't before?
This may be confusing to someone. If so I can explain in more detail.

Also with smithing there are potions and enchantments that say weapon improving 22% better for 60 seconds. Does this mean the stuff where wearing that upgrade or crafted or the stuff your about to smith? Same question goes for the enchantment potion that says enchantments are 22% better for 60 seconds.

On to my last question. Easy probably for all of you to answer. I'll start with saying I was looking to buy a master destruction robe. I went to every single merchant and could not find one. I then went back and they all had pretty much the same stuff as before. What determines when stores get new inventory? Is it a certain amount of days? I have heard that quitting the game resets the store, true?

Any answers would be great. Thank you very much. I apologize for not knowing these simple things. I will admit I am ashamed but I need answers. Happy Skyrim. Go GOTY!