Neil, I'm willing. Just bear with me...

I fired up the old WinXP box, as you suggested. I now have GMAPTool installed. Tried reformatting the 4GB card on the WinXP box- right-click/Format, drop-down only lists FAT32 and exFAT as choices. No FAT16. Tried reformatting anyway, got FAT32, as expected. So...

I checked the 1GB cards... one formatted as FAT32; the second as FAT16. Stuck the 4GB card in again, and XP reported 831MB free and FAT as the format. So I went for it... I hit format. When done, it was 4GB and FAT16! Weird, or what. When I checked the options again, FAT16 is not there... only FAT32 and exFAT.

So, now I have a 4GB card formatted to FAT16, and GMAPTool on the WinXP box.

My next step is to make a copy of the Garmin card. You mentioned RAW copy... any particular method in doing that?