Ep84 near the end: Oscar tells his sister Dolores that ‘Ines hasn’t changed. She’s always been like that’. The text is bolded. It’s showing there’s more meaning behind Oscar’s statement.
Ep93: Oscar and Alicia discuss how Oscar intends to get Ines. During the conversation, Oscar says the following:
SHE'S STILL VERY SMART, AND HER NEEDLESSLY GOOD MEMORY HAS IMPROVED EVEN MORE,
During the Bilbao arc, when Carcel realize Ines was in fact his first wife, it was Oscar who told this truth to Carcel during the timeline when Ines was married to Oscar as crown princess. This shows that Oscar had memories of the original first timeline even back then.

I didn’t read the novel but by how Oscar said that I suspect he retained some sort of memory too. Or I read that in a spoiler somewhere I don’t remember anymore I’m not sure