The lower left corner date is the Original or Amendment date. Changes can happen after that. A major change will cause an Amendment to be done. I don't know exactly what will cause a 'major' change. There are 3 dates on a Chart. In the upper right, above the name of the approach is a 5 digit number. That's the last date 'any' change was made. It's a Julian date. 15344 would be the 344th day of 2015. On the left and right margins are the current issue and next issue date. These are the dates that determine if you have a 'current' chart and I'm sure what Garmin, Jepp et al are looking at to determine 'currency.'
There is this from here
https://www.faa.gov/air_traffic/flight_info/aeronav/faq/
AC 90-100, U.S. TERMINAL AND EN ROUTE AREA NAVIGATION (RNAV) OPERATIONS, paragraph 8a(3): The onboard navigation data must be current and appropriate for the region of intended operation and must include the navigation aids, waypoints, and relevant coded terminal airspace procedures for the departure, arrival, and alternate airfields.
Navigation databases are expected to be current for the duration of the flight. If the AIRAC cycle will change during flight, operators and pilots should establish procedures to ensure the accuracy of navigation data, including suitability of navigation facilities used to define the routes and procedures for flight. Traditionally, this has been accomplished by verifying electronic data against paper products. One acceptable means is to compare aeronautical charts (new and old) to verify navigation fixes prior to dispatch. If an amended chart is published for the procedure, the database must not be used to conduct the operation."
Published instrument procedures and routes are incorporated by reference into 14 CFR Part 95 and 14 CFR Part 97, are "law." They are "effective" only during the AIRAC cycle dates specified on the enroute chart/TPP covers or on the side of the chart when printed from the digital-TPP. If you are using a published procedure before or after the dates specified on the chart under IFR, you are technically in violation of the law.