Experiment tab and collectables
Not entirely sure what you’re saying but I’ll see if I can provide an answer.
1: Discovered items cannot be “rediscovered”, they’re added to your craft list.
2: Different “tiers” of bags require different runes of holding. If you’re making a bag with a higher item tier, you will need a better rune of holding.
3: Only items that can have something be discovered from them by your profession show up in the discovery tab. No need to “discover” a recipe you can’t even use right?
Did any of those answer your question?
You don’t need to “discover” the bag. You already know the recipe. Instead, on the crafting tab, left click the bag. It will show “x bolts of jute, and 1 minor rune of holding” and as long as both are in your bag/bank both will show green, and it will show an option to craft with a # of how many in the bottom section you can make based off the materials at hand.
As mentioned, only items that can be turned into recipes you dont know, will show up as select-able in the discovery screen.
Often if you are trying to craft a safe bag or equipment bag, your crafting level must be higher than creating a regular bag of similar slots.