Yes it is Valid
Per AR 600-8-2, failure to counsel in a timely manner does not invalidate the flag action. Please see the extract below.
Extract of AR 600-8-2
The flagging authority, unit commander, or first line supervisor will counsel all Soldiers on active duty, in writing, upon initiation of any Flag within 2 working days unless notification would compromise an ongoing investigation. Soldiers not on active duty will be counseled regarding initiation of a Flag prior to the conclusion of the first training period following the date the Flag was initiated. Counseling should include reason for the Flag, requirement for Flag removal, and action prohibited by the Flag. All flagged Soldiers will be provided a copy of the DA Form 268 when the Flag is initiated and when it is removed. Notifications for HQDA initiated flags may be delayed to protect against the unintentional early release of a promotion board’s results.2–5. Authentication
Unless otherwise specified in this regulation, only commanding officers, commandants, an officer/civilian with specific authority to sign “For the Commander” (for example, BN or higher executive officer, deputy commander, or adjutant), or HQDA general officer principle staff heads or their designee may authenticate a DA Form 268. Failure to counsel within prescribed times does not invalidate the Flag. The Commander, HRC (AHRC–PDV–PS) will authenticate adverse action DA Forms 268 or investigation DA Forms 268 initiated by HQDA.