In Rosato v. Ricciardi, 174 A.D.2d 937, the Appellate Division dealt with the issue of a late filing in a motion by the defendant to vacate a judgment. In reversing the lower court, the Appellate Division said: "The failure to timely file proof of service is concededly a "mere irregularity" without jurisdictional implications (see, McCormack v. Gomez, 137 A.D.2d 504, 505, 524 N.Y.S.2d 247; McLaughlin, Practice Commentaries, McKinney's Cons Laws of NY, Book 7B, CPLR C308:4, at 311) and may be cured by an order pursuant to CPLR 2001 and 2004. Here, the required proof of service was not filed until the default judgment was sought, well beyond 20 days after the nailing and mailing procedure. Plaintiff did not seek leave permitting late filing until she responded to defendants' application for vacatur in March 1990, at which time she cross-moved for an order permitting the untimely filing nunc pro tunc. By granting plaintiff relief nunc pro tunc Supreme Court not only gave plaintiff a remedy, but made that relief retroactive to defendants' prejudice by placing defendants in default as of a date prior to the order. It also gave effect to a default judgment which prior thereto was a nullity requiring vacatur (see, Red Cr. Natl. Bank v. Blue Star Ranch, 58 A.D.2d 983, 984, 396 N.Y.S.2d 936; see also, Wiley v. Lipset, 140 A.D.2d 336, 337, 527 N.Y.S.2d 829; R. L. C. Investors v. Zabski, 109 A.D.2d 1053, 487 N.Y.S.2d 201; Union Natl. Bank v. Davis, 67 A.D.2d 1034, 413 N.Y.S.2d 489). Accordingly, the default judgment should have been vacated, plaintiff granted permission to file the proof of service pursuant to CPLR 2001 and defendants given an opportunity to answer ."