SDC doesn’t require a new ticket. It is a ticket revalidation rather than a ticket reissue.

in terms of a poug’ed flight, the marker will drop off so I fully expect it won’t work online. However if you did have SDC before the poug, it should be honoured if you call to do it.

I think I did see something recently about that gmt/bst issue - it may be a new issue tho.