Thanks! I thought that was the case. Each wizard is similar to the Vala they served. Yvanna-Radagast, Aule- Saruman. They would have had to retain those memories, personality, and knowledge/wisdom. The wording was a little off. I should have referred to his earlier life as a Maia spirit, before taking human form. Radagast-Yvanna, Aule-Saruman/Curomu, etc.
While Sauron/Mairon was a Maia, and not one of the Istari, he definitely used what he learned from Aule to create the One Ring and to teach Celebrimbor how to forge the other rings.
The only thing that threw me off was what Gandalf says outside of the Door of Durin.
"I once knew all the spells in the tounges of men, Elves, and Orcs. I can only remember a few score of them now." (Probably not what he said word for word, but I'm drawing from memory). I thought he may be referring to his earlier life as Olorien, but he likely just cannot pull the spells off the top of his head. Oloroen/Gandalf had been in Middle Earth for over 2000 years at that point. So I would imagine he can temporarily forget words too.