I have been logging '69 data for decades. These are cars that definitely exist.
My auction db has 2,223 [net] cars, on-line db has 2,787: 5,010. When I combine the auction and on-line db about 7.5% are in both. Net 4,634.
CRG db has data on 7,081 '69s. As Kurt has stated, many entries are data only. Cars not known to exist. Lets call it 33%. So that's 4,673. Of the remainder, 14% of auction/on-line cars are also in the db. So that's 4,020 net '69s.
4,634 + 4,020 = 8,654. Let's say for every '69 known, there are two that aren't: 25,962 including the full range from perfect original to junk. That's a little over 10% of '69 production. I have a hard time believing it could be higher; it is more likely to be lower.
I regularly see new entries on line and in auction results. However, I also see the same cars over and over. 37% of '69s at auction have run more than once; 3-4 times is common. One COPO in particular has been run 8 times. On-line, same story.
I'm no stats wizard so feel free to challenge these numbers.