I hated Ethan being forced as Luke's child (something I feel certain TG insisted upon despite several different creative teams feinting at making him Robert's) and I hate the infidelity retcon they crafted for it, but there was a real interval of time where it would work. Here, just like with Dominique and Mac there isn't so far as I can tell. It's just FV and CVE and co. not caring much about the timeline.
Holly was onscreen in story for almost all of 1992 to the summer of '93. Like Dominique, there was no viable interval in which she could've carried a child to term. Unless they claim she pulled an Adam Chandler and jacked some of that Scorpio jizz from a sperm bank on her way outta town, which while I could buy the more conniving Holly of the last 20+ years doing it, would be once again ruinous to her character.