As Radrick007 said in your other post, the old round pound coins were heavily counterfeited. This was one of the major driving forces behind the switch to the new 12-sided coins.
The Royal Mint stated, in May 2015, that around 2.55% - roughly one in 40 - of all the round pounds in circulation were fake. In May 2014, they had stated that the rate of counterfeits was 3.03% - roughly one in 33. I can't find the exact original survey article (Google links to the modern page speaking about counterfeits of the new 12-sided pound), though there are plenty of newspaper headlines from around that era repeating the statistics.
The Numista catalogue is complete for UK round pounds. You can see the official list directly on the Royal Mint, which is reflected on Numista. https://www.royalmint.com/discover/uk-coins/coin-design-and-specifications/one-pound-coin/
If you have any mis-matched years & designs - they're fakes.
They're worthless. You could probably hand them in at a bank as they still redeem them at face value & they'd probably not notice. Technically, it's illegal to knowingly pass counterfeits but you can probably feign ignorance. However, they're probably more interesting as curios for your collection.
