The major problem faced here is that the general public want a simple description of how the legions were formed, deployed and disbanded. Because of their need for a straightforward narrative, books such as that by Dando-Collins, which purports to give a straightforward narrative, are bought, read and believed by those with a general interest in the Roman Legions. Consequently, any information which goes against the simple narrative are discounted 'because Dando-Collins says so'.
The next stage is that this information passes into 'everyone knows' territory and so becomes accepted as fact, appearing in other books and on TV/the internet.
Hopefully sites such as UNRV can help to correct the spread of false information.