The old Garmin devices such as SP2610 don't differentiate between SDHC reformatted FAT16 and 'original' SD[SC] factory format FAT cards. But that may not be the case for VDO units of course, so trying an original 4GB SDSC FAT16 card would be a very good idea, although it's very difficult to get hold of them now.

In the case of Garmin 'old' units it's probably more correct to say that they don't work with FAT32 or exFAT formated cards [which of course implies SDHC & SDXC cards respectively], but afaik the 3 types of cards are electrically the same and the newer cards can 'adapt' backwardly to mimic the earlier cards depending on how they are formatted [i.e. a SDHC will function as an SDSC when formatted as FAT].