The case of the vanishing (now you see them, now you don't!) decals has been solved. After much online soul searching, trial and error,many test flights, ini editing and finding a complete arabnumber collection in an unlikely long forgotten area; everything seems to be where it is. Once again my friends I salute you for your support, suggestions and experience over the past couple of days. Because of your combined help I can now enjoy my game that little bit more.
Just for the record, I placed all the numbers (00 to 99) in the default decals folder and then edited the decal.ini files for each aircraft accordingly. No need for a decal folder in each skin folder.
Here's to all the contributors in this dicussion.......