Which is not an offence.IANAL, but on the information available to the railway, I think there's grounds to prosecute: their understanding is that a number of railcard-discounted tickets were bought by someone who did not have a railcard.
The Bylaw offence is failing to show a valid ticket on request. As a minimum you would need to have proof of identity of a person stopped, and show they were asked to show their ticket on request, which is not possible.
Nonetheless, the OP is best advised to engage with LNER and be under no illusions that their provided defence, which LNER will have noted from the content of their posts here, is weak. They can still prosecute for the single offence where the OP was stopped, regardless, and may or may not choose to do so.