Hi, you could certainly be right, although there are also sources that confirm that adding the serialnumbers to the Novar's meant the Novar's got outsourced by ICA to Zeiss who again outsourced the Novar's for production to Rodenstock and Steinheil. It is an intriguing story. Also a lot of Icarettes lately are sold on catawiki , maybe a good place to also watch out for.
It's complicated and intriguing indeed! I think we can read every bit of information online, all the books and original documents about the companies and individuals involved, do archeology for 50 years, and we still would have questions left.
When the merger was made in 1926, Zeiss Ikon was formed and it was an independent company, but Carl Zeiss owned the majority of the shares. So it was Zeiss Ikon that bought in the Novar lenses from different makers, not Carl Zeiss. When Carl Zeiss couldn't keep up with production after the war, Zeiss Ikon bought Xenar lenses from Schneider-Kreuznach for some of their Super-Ikonta and 35mm Ikonta cameras.
I don't know if Carl Zeiss made some of the Novar lenses for ICA before the merger, but it's possible. But what is sure is that Carl Zeiss made the ZEISS-ICAR lenses for ICA. (How obvious is that, when it's called "ZEISS-ICAR" and marked "Carl Zeiss Jena"?

) The ICAR was cheaper than the Tessar, so it was probably a three element lens, maybe a rebranded Triotar.
A few Novar lenses after WWII have a red "T", but they are not marked Zeiss nor do they have serial numbers. "T" was the Zeiss coating, so it's possible that the lenses were made by others and later coated by Zeiss. Maybe pre-war stock, or from manufacturers that hadn't started doing their own coatings yet.
While the Novar on the Icarette is good, the four element/four groups ICA Hekla or Litonar should be optically better, albeit with lower contrast. The Tessars are of course good, but so common. The top of the line would be the Icarettes with the six element/two groups ICA Doppel-Anastigmat Maximar or Zeiss Doppel-Amatar. Vintage camera users don't pay much attention to the ICA Maximar lens because it's an in-house ICA lens and thus it feels generic. But it is a copy of the famous Goerz Dagor.
