LUSID generates journal entry lines in response to economic activity in underlying portfolios. Journal entry lines are stored in a dedicated store.
When you close or lock a period, LUSID persists all the journal entry lines associated with that period. It is not possible to change this data unless you re-open the period.
LUSID generates valuation point data when you value a fund at a particular moment in time. Valuation points, and the data associated with them, are stored in a dedicated store.
When you finalise a valuation point, LUSID persists all the data associated with it. It is not possible to change this data unless you explicitly delete the valuation point.
In summary: You can always recreate a report based on a closed/locked period or a valuation point. The persistence mechanism is future-proof against code changes in LUSID itself.