Engine Sound Mat Plugs, Yet Another Mystery - 3 or 4? Options

[StarBear]

OK; as I'm continuing to comb through various tidbit parts, I've come across this mystery (to me). Asking for any insights, experience, or wisdom.

The engine sound-deadening mat has several plastic attachment plugs, part # 914 559 377 10; on PET Section 8, Diagram 807-10, #14. It has a barbed plug end and the PET (and other sources) show 4 are required. See photo.

Yet, mine (largely unmolested) has only 3. See photo.

There are two other holes along the left wall and right wall (hidden by the battery), the backsides of what I presume are the seat belt retractors, but these are wide and are filled in by the bolt end - nowhere for a barbed tip to attached. BTW, I've been using more of a mushroom cap to cover them. See 3 photos.

Question 1: If four are used, where the heck does the fourth one go??
Question 2: Might four have been used in early (70-71?) models and PET, etc not updated?
I'm so very confused.

Plastic Plug:


Three plugs holding mat:


Larger holes from seat belt (?) bolts:



Mushroom cap I use: