Mathematically, a true 620-in-1 would require more memory than the NES’s bank-switching architecture could reasonably manage with 1990s economics. Most authentic 620-in-1 carts contain roughly of actual data, padded to a 620-number menu.
In Brazil in 2005, an original Super Mario Bros. cartridge cost the equivalent of $80 USD. A 620-in-1 cost $15. 620 In 1 Nes Hack
The NES library consists of games ranging from 40KB (early titles) to over 1MB (later RPGs). Fitting 620 full-sized games onto a chip would require massive storage capacity, which would drive up the cost of the cartridge. To keep costs low, pirates employed aggressive file compression and "trimming." Mathematically, a true 620-in-1 would require more memory