If you buy a Navionics chart card for the entire US and Canada, it comes with a year of online updates via the web app. You can renew the annual update subscription for a fee, so your CP is always up to date with recent data. The web app lets you select a rectangular area to update, but the data limits of the card restrict you to a regional area. So, for example you could select the area from NJ to Maine, or the Southeast, but not both.... a limiting issue for "snowbirds" doing the ICW.

I found that by selecting smaller, overlapping rectangles, I was able to select the entire US east coast including Key West and the northern Bahamas. After you select and download an area, the Navionics web app lets you add another area, and you can keep doing that with additional smaller areas so long as your card isn't full. (I excluded the "Community Edits" data because the CP isn't my go-to device for that type of info, I prefer using the iPad and PC/Coastal Explorer apps for that type of info including ActiveCaptain data).