firstly, per IEC 62304 does not mandatory Agile/ V model. it at the discretion of the device manufacturer to adopt.
a) that, once adopted (if Agile) then, software development plan can state the model and documentation strategy adopted to fit Agile way.
*documentation strategy: can must essentially follow Document control procedures + look at industry standard practices such as:
a) In Sprint documentation and reviews (SW Development plan, URS, SWRS, HLD, LLD, Unit Test procedure, SW sub system Test Procedures, System test procedures etc)
SW Test Plan needs to document to strategy (acceptance criteria) for each level of test (including Unit tests) performed during in-sprints.
Finally, SW development plan can highlight the acceptance criteria for in-sprint.
* in-sprint - first 2 sprints can be development and unit tests, next following sprints upto 6th sprint can Verification scripts followed by approving SW release letter.
let me know if this clarifies your query.