The 3 hour rule is an IATA standard; airlines can choose to outperform that, but they can also choose to reject ticketing closer than 3 hours to departure. The profitability of the ticket might colour their decision. I've bought dozens of tickets less than an hour of departure time (either by phone or at the airport), so this would be a big impact if it was enforced. Remember that IATA member airlines have to vote on all these standards.

All airline tickets have 12 month validity from date of issue, and a further 12 months from date of first segment travelled; so up to 24 months. Useful if a large fare increase is imminent! 550 days is cutting almost 25% from that!