And this from the IRS:

Is identity verification a one-time event?

No. Identity verification must be completed every time a taxpayer electronically signs Form 8878 or 8879, with two exceptions. If a taxpayer e-signs the form in the physical presence of the ERO, and the taxpayer has a multi-year business relationship with the ERO, then no further identity verification is needed. A multi-year business relationship is one in which the ERO has originated tax returns for the taxpayer for a prior tax year and has identified the taxpayer using the identity verification process.

https://www.irs.gov/e-file-providers/frequently-asked-questions-for-irs-efile-signature-authorizatio...