Okay at least I now understand
What would be good as a feature (and in the main product) would be the notion of cycling out backups by time as well as day retention as is now the case as even using my example as a reference.
Taking my above example, the time you start to use the USB that has been out of circulation for a year, the notion of having it do another incremental might be quite contrary to what you want given that the server has probably been used quite a bit in the last year. It would be good if you could say that for example if a backup chain is more than 3 months old, consider it 'stale' and of no use and start a new one.
Is there any issue in implementing such functionality manually via a script before my backup runs? For example check the age of the files on the USB and if they are greater than XX days, simply delete them. Veeam would then come along to run the backup, realise there are no backup files on the USB and then start a full backup again. Is there an issue with that logic?