Looking at what Mrs Beckham tends to wear (such as in her latest pictures,) she can make even the softest implanted breasts look firm. It is hard to tell with this kind of clothing.
I’d still lay my bet upon her having had them re-done late last year but there is not much that is certain when you examine images of clothed celebrities alone. That is what makes this so interesting, yes?
It is also possible that her new implants have started to “firm up.” Contracture commonly recurs particularly in women who smoke and women who had silicone gel implants. I do not know the specifics in her case.