The tag no.s should correspond to the holding of origin, and they would normally keep those tags for life wherever they go.
If they're not going for slaughter, then ideally the holding of origin should have given them double tags (with an EID) if they're not going for slaughter within 12 months - I'd have thought they should have had those if they were going to be sold off the holding before 12mths also, but I am not certain of that.
I guess if you cannot get double tags from the holding of origin: if your sheep were to 'lose' their tags you could order up some double-with-EID 'replacement' tags which would have R and your flock no. on them; although I can't help thinking that's a bit of a naughty way of doing it.