This site (although incomplete and sometimes frustratingly worded) might be of interest:
https://www.apple1registry.com/There have been Apple-1 clones made, but they are apparently not too difficult to identify according to private communication with the site maintainer. It appears that some known clones are on exhibit today. Validation is typically performed by one or more methods:
1. Owner's statement, possibly with bill of sale.
2. Checking the Byte Shop-added inventory number / handwriting against a known sample, if it has the number.
3. Board masking and inspection stamps.
4. Board logo if it's from the NTI batch.
5. Date codes and lot numbers of passive components on the board - they are known, and difficult to replace/alter without leaving evidence.
My friend's Apple-1 was bought during the time when they were still on sale at small computer shops, so there would have been little to no incentive to make a clone and try to sell it at a shop which already carried the legit items. They weren't so popular as to be worth the cost of having a then-expensive custom board layout manufactured. He can trace it back to Apple with some certainty, and it passes the inspection steps above. That, plus Woz examining the item personally, makes him pretty sure it's real. It should be straightforward to validate any true unit - it's unfortunate that info wasn't shared, but any details might unwittingly help a counterfeiter so I can see why they might not broadcast it.