The first paragraph is correct, but the second isn't - for a journey from e.g. Abbey Wood to Heathrow using the EL, you could use a Zone U1234 to Heathrow Rail ticket. This is simply the result of the first paragraph!I'm not sure that this information on Elizabeth line fares sent by TfL to MPs and London Assembly members is quite right (or if right, it's not as clearly expressed as it could be). It certainly does little to demystify ticketing!
Source: https://twitter.com/JuliaLopezMP/status/1588797742209458176
The last paragraph represents TfL's made-up policy (which has no basis in the NRCoT) that the EL magically ceases to be a National Rail service in the core. There are quite a few tickets issued to London Terminals (or other tickets without a Maltese Cross or U Zone validity) which are valid on the EL core.