Mod A & B both reference a character, & mod B changes some of the stats. That's fine. However, mod A also adds a new weapon to the character, and mod B leaves that entry blank. If mod B is loaded after A, is the blank entry used and the weapon defaulted to vanilla, or will the new weapon of mod A prevail?

You will only see the changes from both mods if you use Wrye Bash to create a bashed patch, otherwise, the character as represented in the mod that loads last, will be what you end up with in-game.

Thanks for the quick response. I was unsure, since sometimes both mod A & B will not edit a vanilla part of the character, thus I didn't know if the blanks meant the entry doesn't happen, or simply default to vanilla.

Even though there are many different things about an NPC that can be changed, all of those things are still part of one single record. So that's why it's all from what the later-loading mod says, and none of what the former-loading mod says - blanks included. It can be a very frustrating fact to work around, but as HeyYou pointed out, that's what Bashed Patches are for.

So wait. If a particular part of the entry is left blank by both mods, will it use the vanilla setting or nothing at all?

It will use the last loaded.

And remember, the save game file is the absolute last loaded thing. So if its a persistant reference object, it may even be part of your save game now and mod changes will not affect it anymore.

Depends on what you mean by "left blank". If you blank out all the entries in the record, then the record will be present but empty in-game, because it will be marked modified to be empty in your plugin. If you don't modify the record at all, then your plugin will not contain any data about the record, and you will see the vanilla object in-game.

In your opening post you mention "adding a weapon" to a character. That can be done in two ways. The inventory on the base form can be changed, in which case another mod can undo that change.

The other method is for a quest script to do an AddItem to place it in the character's inventory after the game has loaded. Typically, that function is inside a test on GetGameRestarted, and another to see if the item is already there, so it runs once and does not create duplicates. This works even if another mod disables the character, but it's a bit moot in that case!

Khettienna, that's what I was looking for And ghastley, also good info. This is definitely base form editing and not script based. This is the situation I am faced with;

Oblivion...............Mod A...............Mod B
Vanilla Weapon
...........................NewWeapon A1
....................................................NewWeapon B1

as opposed to;

Oblivion...............Mod A...............Mod B
Vanilla Weapon....Vanilla Weapon.....Vanilla Weapon
...........................NewWeapon A1
....................................................NewWeapon B1

So the way I understand it, if a vanilla record is untouched, it remains the same. But mod-added changes will be undone if a later mod doesn't include those changes or use a Bash Patch to import.

...provided the later mod does indeed include that record. What you absolutely should do, is to open the two mods and the Bashed patch together in TES4Edit. Navigate to the record in question and click on it. It will then in the right-side pane list all mods that touches that record and how they affect the record, with color coding that helps you easily indentify when a mod is overriding/conflicting with another.

But ghastley's advice is sound - except that the test should be done within GetGameLoaded and not GetGameRestarted, or there may be other, more natural times doing it. I add bedrolls and kaffee to merchants in Real Sleep Extended, and all types of quest items to containers in Enhanced Economy, but in both cases I do it the moment the merchant/container is activated. That way there is no conflict with any mod that changes those merchants or containers, and my mod is even load order independent.