Simple Q&A D&D 3.5 (by RAW) XXIII

[Lord Il Palazzo]

A 520c (clarification of 520a)
This was already answered:

That was my error; I got distracted and posted before finishing the explanation. The original post has been edited, with clarifications added in red. I apologize for the confusion.

A 520d (clarification of 520d)
These are the same, excepting some special abilities which alter the normal actions available in a round. You can either use a standard action for a single grapple check in place of an attack, or a full-round action for as many grapple checks as you are allowed attacks in a full attack. In either case, you are allowed only one action in the round which permits you to make grapple attacks. The limitation of attacking with only one weapon while grappling then becomes a limitation for the round.

Okay. I'm going to try this one more time. You're quoting around and ignoring the central points of my questions. I am underlining the parts I want answered. Please quote and respond to them. I am asking for citations. Book names and page numbers, SRD links, anything that shows that what you're saying is actually from the rules rather than just being your interpretation. If you can't give any citation for what you're saying, just say so and I'll appreciate your honesty but please don't just tell me "this is how it works" and try to leave it at that; it's not what I'm looking for and it's not a helpful answer.

Q 520e (final clarification to Q 520a)
When the rules refer to "extra" damage, they refer to damage in addition to other damage not in place of it. The "extra damage" from a sneak attack sneak attack doesn't replace the base damage. (A derro's racial sneak attack for example deals "+1d6" damage, not just "1d6".) Neither does the "extra 1d6 of fire damage" from a flaming weapon. (Note that the Balor's +1 Faming whip does both the 1d4 whip damage and the 1d6 fire damage.) When an attack's damage die is replaced entirely (such as by the monk class's unarmed strike damage progression) the word "extra" is nowhere to be seen.

Is there any RAW basis for treating the "extra piercing damage" when grappling from spiked armor as a replacement to normal grappling damage rather than an addition, even though every other instance of "extra damage" is an addition?

Q 520f (final clarification to Q 520b)
Your previous answer ignores the fact that it is possible to make multiple things in one round while grappling, which aren't necessarily the same but are each referred to as an "action". Quoting the rules, from here:

If your base attack bonus allows you multiple attacks, you can attempt one of these actions in place of each of your attacks, but at successively lower base attack bonuses.

So I will ask again:
Is there anything actually written in the rules to support applying the "can't attack with two weapons while grappling" limitation round-by-round, even though it's written as a limitation of a particular action ("Attack Your Opponent") rather than a limitation of grappling as a whole?