On another quote, Fr. Feeney said he didn't believe adults go to Limbo. But St. Ambrose spoke of martyred catechumens who died without the Sacrament as having been washed (of their sins) although not crowned. So where do these martyred catechumens end up ... in hell? Even though they have had their sins washed? Lacking person sin (and the punishment due to it) is precisely what Limbo is all about. Matto pointed out that Dante put some adults in Limbo. Not that Dante was a theologian, but I guess he reflects some theological thinking prevalent in his day. I don't see anything contrary to Church doctrine in positing adults in Limbo.
Now, could some of these Catechumens have been actually baptized by having the angels pronounce the words of Baptism, as St. Cyprian believed and was also taught in that 5th century theological manual? Perhaps, but St. Ambrose doesn't seem to believe so. It's speculation, really, after the point of what has been revealed. And what has been revealed is that the Sacrament of Baptism is necessary for salvation, even if not for justification.