Why wouldn't I? TOC was a Pro Slam, according to Karoly Mazak and his pdf, The Concise History of Tennis. I counted all slams.
It is, in my opinion, the most fair way to do it. Many years there were split #1's.
If we see the year end champions from open era, we can note that take all weeks of a calendar year is not the rule. IMO the same ocurred pre open era.