I have delt with C-Map out on Cape Cod. Here's the problem with trying to install "New" cards in an OLD GPS. They, C-Map and everyone else doing GPS support are continually updating their cards as hardware becomes more capable. C-Map does not keep old files for chips that were made by them for more than a year or two if you are lucky.
Technology is changing rapidly. The new cards have so much more data on them that "OLD" GPS units simply do not have enough
memory or
speed to handle it. The Card may actually fit, but the GPS unit can not handle the added data on the card.
NB