Good for you for trying to sort this out. Seems like an impossible task though unless, As has already been mentioned, you have a very large amount of money to toss around and get some real accurate DNA testing done.
I'm no expert but from what I have read varieties of figs will change. The change can be caused by FMV or amount of FMV. Soil conditions, USDA hardiness zones, fertilization, age of tree. I'm sure theres other factors as well. I've seen this with other species of plants as well. They change and adapt depending on climate elevation, grower, fertilizers, ect..
Start a post and ask everyone who is growing VDB to post a photo. My guess is you can get a general concensus as to what the leaves are supposed to look like but nothing concrete. Same with flavor profile. Of course thats very subjective anyway.
Add to that the fact that there are probably thousands of varieties already and everytime a bird poos a new one is created. My guess is that in the US we may have 10-20% of the figs available worldwide. If you are able to catalog 100-200 varieties thats a monumental task in itself and worthy of doing if you are that dedicated to it.
When this project is complete, we will be able to identify ANY variety and see, also, that the list of varieties might shrink drastically. There will be almost no Unknowns if the information is used correctly. There aren't many mutations and new breeds of figs that humans don't already know about, but there are many, if not all fig varieties, that behave differently under different conditions and circumstances of growth.
I think your looking at this from a US perspective. You may be able to get this info for known US varieties but not for all varieties of the world. Not in one lifetime anyway.
How many varieties are there in Italy, Albania, Greece, the middle east, Asia, Russia ect.. Some may have made it here but for every one that does there is probably 10 that doesnt. If not more.
Again this info will be usefor for those of us in the US but for someone in portugal, maybe not so much. They may have 50 trees that we have never heard of.
I was looking through the grin database of grapes the other day. I think theres almost 1900 varieties. Figs less than 400 listed. How many are listed from Albania? Maybe 10 and theres probably 100 or more just in that one country alone. In Turkey there may be 100's as well. Granted some of them may have made it to Albania but just by looks and taste alone we will never know. And thats the real point. Unless you can do the DNA testing this will never truly be accurate.
Look at the confusion that already exists between the varieties in the US. I think also that less than 1/2 of them have even been released to the general public.
One thing I would suggest is see what countries have similar systems in place like our USDA germplasm repositories. You may be able to contact them in each country and get a list of the information they have available. If you can get a list from each country with photos of leaves and figs then you can at least do a visual analysis.
My guess is you will need 10-20 years if your going to do this on a worldwide basis. And thats full time work. As a hobbyist my guess is next to impossible. If you really want to do this though maybe look into writing a book and getting some sponsorship money to fund the project.