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If you send a DV within the 30-day period for verification set by their dunning notice, it imposes an automatic cease collection bar that prevents them from continuing collection activity, including reporting to the CRAs, until such time as they have provided the requested debt verification.
The "it will be presumed valid" statement is part of the statutory provision for dunning notice (FDCPA 809(a)), and is just that.... a presumption on their part.
It is not a basis for establishing its validity in court, and is not something to be worried about.
If, in addition to seeking verification of the debt itself, you have other issues concerning the accuracy of any reporting on their part, you can additionally pursue a dispute under the FCRA.