Umm, didn't everything change with Christ? So, that what happened before Christ no longer pertained as he instituted the sacraments.
Yes, but the same principles apply. In God, there is neither shadow of change nor alteration. He operates in the same way, always, despite the fact that he uses different instruments at different moments.
The point is: People WERE being justified outside of the sacramentally-prefiguring Mosaic prescriptions.
By calling it all "irrelevant" or "imprudent" is simply ducking the question. St John, for example, was certainly justified in his mother's womb,
not through circuмcision (which was gfranted efficacy with a view to, and through, Christ's merits), although he would undoubtedly have been circuмcised when born.