Ya so then to me say you have 30sdi on your stat total which the game shows you and you add 100 inscription to your template, shouldn't your new total shown on screen by the game total to 40 under the sdi section? That's the way it seems it should work but it isn't adding to the total which I think is a bug. If you use arcane empowerment it adds to ur sdi total when used so why not inscription? Unless I'm missing something here.
In a way you are correct, I DO understand your confusion. The problem is, the character status like many things in UO is very inconsistent and user unfriendly.
Lets talk about the Character Status window in the Classic Client:
Its shows you actual STR, DEX, and INT, it shows your actual base weapon damage output based on your anat and tactics and str etc and your actual actual lower mana cost and that will not exceed the lower mana cost cap. This is all fine.
Now everything else is kinda just item based display:
Hit chance increase: It will show the total amount of HCI you have on items, it won't show your actual chance of hitting something because this depends on what you're hitting, but if you get hit by HLA this will indeed drop. And the hit chance increase won't display above the current in-game cap.
Defense chance increase: the rules for the display for this are the same as hit chance increase.
Damage increase and swing speed increase. Again this is item based, errr ok in stone form the display will show a drop in swing speed and casting and raise in resist but won't display the increase of damage increase? (think this bug has been submitted)
It won't show your actual swing speed as this depends on the weapon you are carrying and your stamina, perhaps there should be a separate display for that.
OK so we've got 2 displays for output of damage. You have damage, and you have damage increase. Perhaps then for spells there should be spell damage and spell damage increase so you can see your base spell damage. But then what figure would this actually display? Because the damage shows the damage you would do with the weapon you are holding on a creature with 0 resist. But spell damage depends on what spell you will cast so it's perhaps not practical to display a base spell damage. But needless to say, if there was a base spell damage display, it would indeed show this 10% increase you have from inscription.