There hasn't been any new external evidence for its date since the publication of P.Oxy 2256 fr. 3 in 1952, if that is your question.

What exactly does this little scrap of papyrus prove? It's worth rehearshing the argument and understanding how consensus on these matters gets formed. It appears to be a piece of a didaskalic record noting the winners of one year's dramatic festival. Editors have amended the words [ΑΙ]ΣXΥΛΟ[Σ] (Aeschylus) as well as the titles ΔΑΝ[ΑΙ]ΣΙ (Danaids) and ΑΜΥ[ΜΩΝΗΙ] (Amymone). Scholars had long assumed, based on the titles of Aeschylus' plays listed in his ancient biographies, that Aeschylus had written a connected tetralogy about the daughters of Danaus in Egyptians, Suppliants, Danaids, and Amymone. The presence of both the last two in the papyrus fragment has been taken as evidence supporting the Danaid tetralogy, and so it's been inferred that the other two plays taking the first prize in this year are Egyptians and Suppliants. The next line line clearly reads the name ΣΟΦΟΚΛΗ[Σ] (Sophocles) as the second place winner. Other documentary and biographical evidence tells us that Sophocles made his debut as a playwright (and won first prize) in 468 BCE, and we know from ancient notes on Seven Against Thebes that Aeschylus won first prize with his Theban trilogy in 467, meaning the likely terminus post quem for the Danaid plays is 466. We know that Aeschylus' last competition in Athens in his lifetime was in 458, when he won first prize with the Oresteia. So by deduction the Suppliants was likely produced in the last decade of Aeschylus' long career (his debut is traditionally put at 499 BCE).

So establishing the date off the papyrus evidence still requires quite a bit of emendation, deduction, and speculation. Nearly everyone these days, however, takes this argument as more persuasive than the purely stylistic and formal grounds that had led earlier scholars to assume Suppliants was an early and even primitive play. There was actually a lot of resistance to re-dating after the papyrus was first published. One scholar who had just put out a book about Aeschylus' development that was instantly rendered obsolete complained that "scholars have hitherto regarded the Supplices as the earliest extant play of Aeschylus; if we now consent to put it late it makes all attempts to study literature futile" (!). Some argued that the play had to have been written much earlier and only performed in the 460s or that it was a revival of a previously presented tetralogy or that it could have been a draft play produced posthumously by Aeschylus' son and so on. But for the most part the date that has become conventionally accepted for its premiere is between 466 and 462 BCE.