Thomas A. Bergstrom argued that the pre-2007 version requires direct personal supervision of a child. But as the Archdiocese of Philadelphia's secretary of clergy - responsible for investigating complaints against priests and recommending discipline - Lynn was only a "supervisor of a supervisor," Bergstrom said.
Bergstrom said the post-2007 law, which enabled prosecution of church officials for crimes committed by priests they supervise, cannot be retroactively applied to Lynn, who left the clergy secretary post in 2004.
"We can all still understand and read and write the English language, and it says what it says," Bergstrom told the judges.
Assistant District Attorney Hugh Burns, chief of the office's appeals unit, said Bergstrom's interpretation of the pre-2007 statute was too narrow.
"It's much broader than simply having direct supervision of a child," Burns argued. "It's supervising the welfare of children."
Burns told the judges that the law required Lynn to protect children from pedophile priests by not allowing them to be assigned to posts where they had access to - and would likely prey upon - children.
The judges gave no indication Tuesday of when they would rule.
Judge John T. Bender seemed especially interested in Lynn's sentence and how long the 62-year-old monsignor has been in prison.
In July 2012, a Common Pleas Court judge sentenced Lynn to three to six years in prison after a 13-week trial and 121/2 days of jury deliberations.
Lynn was denied bail pending appeal and has spent most of the last 15 months in Waymart Prison in Northeast Pennsylvania. He is eligible for parole in 15 months when he completes his minimum sentence.
Bergstrom said afterward that he was encouraged and that Bender's focus on Lynn's sentence might mean the court would expedite its decision.
The wood-paneled courtroom was packed to standing room with lawyers, priests, and some sex-abuse victims. Among them were lawyers for others - including three priests - charged with Lynn after a 2011 grand jury report on sexual abuse in the Catholic Church.
The three judges - Bender, Christine L. Donohue, and John L. Musmanno - peppered the lawyers with questions during the half-hour argument.
Bender and Donahue, for example, asked why Lynn was prosecuted under the pre-2007 law when a Philadelphia grand jury in 2005 said he could not be prosecuted.
Moreover, Bender noted, the law was amended in 2007 principally to correct the earlier grand jury's inability to bring charges against Lynn.
Burns disputed that interpretation, saying: "Sometimes the legislative purpose is to clarify and reinforce the intent" of the original law.
Burns also argued that just because a case like Lynn's had never arisen before does not mean Lynn could not be prosecuted under the pre-2007 law.
Contact Joseph A. Slobodzian at 215-854-2985, firstname.lastname@example.org, or @joeslobo on Twitter.