Why Peter and Catherine's marriage date matters

Is the uncertainty over whether Peter I and Catherine I were married normal for this period?

A later public marriage is documented, but the earlier secret marriage is uncertain; without it, their children's legitimacy and succession rights could be challenged.

The surviving historical account includes a later public ceremony but leaves uncertainty over whether an earlier secret marriage occurred before their children were born. That ambiguity matters because legitimacy shaped eligibility for the throne. The earlier marriage may have been retrospectively regularized in the record.