If I sign the Declaration of Continued Airworthiness before the expiry date of the current NARC, which expiry date would apply to the new certificate?

If the Declaration of Continued Airworthiness is signed within three months prior to the expiry of the NARC or the previous declaration, the pattern shall be maintained and the two years shall be counted from the date on which it was due to expire.

See graph below:

Otherwise, its validity shall be calculated from the date of signature of the declaration: