The "total minted" and "known melted" are well-documented quantities from US Treasury/Mint records and limited foreign bank records.
"Total known survivors" comes from post-WW II physical counts of looted gold and coins restored to rightful owners; plus estimated extant collectible pieces.
"Theoretical survivors" are just that: theoretical. It is not known what happened to these coins. Most were probably melted and recoined after export from the US as part of business and international loan transactions. During WW II Germany and Sweden melted coins and bars so they could be reassayed and freshly stamped - this avoided questions when the new bars were offered in payment for war materials to Portugal, Switzerland, Spain and others. Small hoards remain in France, Belgium, Netherlands, and elsewhere in Europe, but they do not constitute a significant quantity. (These will "pop-up" with generational changes.)
The situation is better documented than for Liberty DE, but the unknowns are large and probably undiscoverable.