MailStream Plus questions on Unique addresses and position 26 of the ALG CR parameter

Since the ALG CR parameter position 26 defaults to Y, when does the USPS care if the address is unique or not?

The MailStream Plus user was told that the USPS doesn't care if you have more than 1 record to the same address when qualifying for High Density.

This is true.  When presorting a Standard class, Letter presort, here are the DMM rules:

DMM - this For High Density

6.4.2 Basic Eligibility Standards for High Density and High Density Plus Prices for Letters
All pieces mailed at high density or high density plus prices must be prepared in walk sequence according to schemes prescribed by the USPS (see 245.9.8 through 245.9.9). Multiple pieces per delivery address can count toward both density standards....

But for Saturation the rules only count each address once for letters to the same address.  And positio 26 of the ALG CR parameter applies to Saturation prices:

6.6.2 Saturation Prices for Letters
All pieces mailed at saturation prices must:
b. Meet the density requirement of at least 90% or more of the active residential addresses or 75% or more of the total number of active possible delivery addresses on each carrier route receiving this mail. Pieces bearing a simplified address must meet the coverage standards in 602.3.0. Multiple pieces per delivery address do not count toward this density standard.

Using the ALG CR parameter, position 26, this defaults to Y -

Y Attempt to qualify the walk sequence saturation rate based on the unique address only.
If this is changed to N, MailStream plus will not follow the current USPS rules.

N Do not attempt to qualify walk sequence saturation rate based on unique address only.
blank Default is Y.

When using the N, it is best this is only during testing and not for a production job. 

The above DMM rules are current as of April 2015.  

UPDATED:  April 5, 2017