I'm trying to grab information about NFT-to-ERC20 swaps conducted over 0x V4 (on Ethereum). My initial intention was to read ERC321OrderFilled events from https://etherscan.io/address/0xdef1c0ded9bec7f1a1670819833240f027b25eff. However, it appeared that there are very few of them - only a few hundred starting block 17000000, for example. My assumption was that this scenario (swap NFT to ERC20) should be very popular for OTC sales, and I'd expect much more transactions with ERC721 orders. So I wonder if that's the right direction to find such swaps. Otherwise, what event will be generated in a typical NFT-ERC20 swap?
Another assumption - V4 is just not used for such swaps in general, and it is rather worth looking for older versions - V2.1 or V3.
Any advice would be appreciated.