It seems like when we file i131 together with i821, we can send them all to the same address; so one copy of those documents should suffice.

Secondly, I thought, Notice of Action i797 is only needed for I-131 based on a pending or approved Form I-821,

Is this not so ?

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I checked the following website
https://www.uscis.gov/i-131-addresses

If you are…
- Filing Form I-131 together with a Form I-821, Application for Temporary Protected Status

Send your form to…
- The address listed for on the TPS page for your country
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If you are…
Filing Form I-131 based on a pending or approved Form I-821,
You must include a copy of the receipt notice (Form I-797C) showing we accepted or approved your Form I-821.

Send your form to…
USCIS Dallas Lockbox
For U.S. Postal Service (USPS):
USCIS
Attn: I-131 TPS
P.O. Box 660167
Dallas, TX 75266-0867

Source
https://www.uscis.gov/i-131-addresses