Unlike AIRACS, charts are not issued every 28 days, but only when something in the procedure changes. For those who use printed Jepp charts, there will be an index in the chart book that lists the current effectivity number for each chart. Rather than paper charts, our flight department uses JeppView on two separate iPads, and the charts are also available on the MFD of the aircraft (with current position overlaid).
I have ridden in the jump seat in our company aircraft many times. The pilots’ main concern when selecting a particular chart is to insure that both are using the same effectivity number.
The charts stored in the aircraft avionics are updated from a laptop using a data file downloaded from INDS, which is a joint venture between Jeppesen and Honeywell. The pilot iPads are updated directly from Jeppesen by logging into our company account.
Each iPad electronic update includes an electronic copy of the master effectivity index, and if any chart on the iPad is not the latest revision, it will give a warning. The aircraft update used to install a fresh copy of all charts, every time it was run which was quite time-consuming. The new system only installs those charts which have actually changed since the last update, so the update process is much faster. This is similar to the process of updating paper Jepp charts.