It looks to me like your game is working correctly.
Experiment:
I just tried your Iron Dagger experiment and saw similar results. The problem is that the Iron Dagger base numbers are so small a 25% difference was within 1 damage point. I tried the same experiment on an Ebony Sword (for which I do not have the Ebony Smithing perk) and I saw a difference of 5 damage points from the extra +25% Smithing gear.
Solution:
If you really want to improve that Daedric Bow, you need the Daedric Smithing perk. Or... you know, a game-breaking level of +Smithing gear/potions.
With help from cyrus224 at Nexus Forums:
Walk up to Hert and press the ~ key at the top left of your keyboard to open the Console.
Click her, then type the commands listed below.
Or you can copy and paste the code into Notepad.
Scripts must be in the same folder as TESV.exe
C:\Program Files (x86)\Steam\SteamApps\common\skyrim
To execute a script type the following command into the Console:
BAT scriptname
where scriptname = the name of the script file
Example: Bat VampireCureHert
How to Cure a Player or NPC with Vampirism
Choose a RaceCode. Don't execute this command if you want them to continue looking like a Vampire (or you could execute this code just to change how Hert appears and NOT cure her).
SetRace NordRace
Then you need to run all of this code, which is why it is suggested to do it in Notepad.
AddToFaction 000C4DE0 -1
AddToFaction 0002EB13 -1
AddToFaction 00046281 -1
AddToFaction 00027242 -1
RemovePerk 0010F1EC
RemovePerk 000F5B56
RemovePerk 000CF02C
RemoveSpell 000F5B54
RemoveSpell 000ED0AA
RemoveSpell 00107AA1
RemoveSpell 000F5B58
RemoveSpell 000F5B59
RemoveSpell 000F5B5A
RemoveSpell 000F5B5B
RemoveSpell 0008D5C3
RemoveSpell 0008D5C7
RemoveSpell 000ED0A9
RemoveSpell 00088821
RemoveSpell 000ED097
RemoveSpell 0010F1E7
RemoveSpell 000ED0A8
RemoveSpell 0002E1C3
RemoveSpell 000ED099
RemoveSpell 000ED09D
RemoveSpell 000ED09E
RemoveSpell 0010FB30
RemoveSpell 000F5B5C
RemoveSpell 000EA077
RemoveSpell 000EA078
RemoveSpell 000EA079
RemoveSpell 000EA07A
RemoveSpell 000EA07B
RemoveSpell 000C4DE2
RemoveSpell 000ED0A4
RemoveSpell 000ED0A5
RemoveSpell 000ED0A6
RemoveSpell 000ED0A7
RemoveSpell 000C4DE1
RemoveSpell 0008D5BF
RemoveSpell 0008D5C0
RemoveSpell 0008D5C1
RemoveSpell 0008D5C2
RemoveSpell 000ED0A1
RemoveSpell 000ED0A0
RemoveSpell 000ED0A2
RemoveSpell 000ED0A3
RemoveSpell 0010F1EB
RemoveSpell 0010F1EA
RemoveSpell 0010F1E9
RemoveSpell 0010F1E8
RemoveSpell 000F5B5D
RemoveSpell 000C1E8B
RemoveSpell 000ED09A
RemoveSpell 000ED09B
RemoveSpell 000ED09C
RemoveSpell 000B8780
Best Answer
Step 1
Complete the quest "A New Order".
Step 2
Make sure you have the Steel Smithing perk & talk to Sorine Jurard. She should train you in constructing a basic crossbow & steel bolts.
Step 3
Locate Gunmar's Forge, you'll need it to craft most crossbow & bolt recipes in much the same way as the Skyforge is required for Nord Hero gear.
You can now start making bolts
Step 4 (Optional)
Complete an Ancient Technology quest for Sorine. Your reward will be plans for either an improved crossbow or exploding bolts. When you start getting plans for dwarven gear, get the Dwarven Smithing perk if you don't already and you plan on using them.
Repeat Step 4 until you have common & enhanced crossbow recipes and common & 3 elemental bolt recipes, all in both steel & dwarven varieties.