Go looking on torrent feeds like pirate bay there is usually a fairly complete CM93 R2 iso to be found.
Only issue I have seen is that you might need to merge the DVD
iso contents onto the HDD in a single
directory you run your Open CPN
charts to get all the detail to flesh out reliably no matter where you go in the world. leaving the data in separate regions seems to suffer as you say from missing detail otherwise.
There are some boundary merging issues overlaying the chart set on high zoom / over zoom but in practical sailing terms usage I have personally not seen anywhere that the one from the torrent would not allow you to navigate anywhere in a pinch. Only caveat as always is making allowance for shifting banks due to tide and erosion. I have a set of local Navionics
charts that I have done a cross comparison on including the usual routes on the East and West Coasts of the USA Incl Panama
and it seemed to me to be very comparable.
Good Luck with your quest and if you find anything more detailed in open source let us know