What does 'Locked till …' or 'No lock date' under a company's column mean?

Under each organisation's column heading on Financial Reports Saral shows that organisation's Xero lock date, read live: 'Locked till <date>' means nothing dated on or before it can be posted in Xero; hover for the two dates (all users except advisers, and all users) and when it was read. 'No lock date' is a reading, not a gap. '(Xero did not answer — last known)' means the last reading was used. The link opens that organisation's financial settings in Xero; Saral never changes a lock date.