Thank you both for your appreciative comments.
Some commentators have chosen describe the original 1998 WTB NanoRaptor tire as the first true 29er tire. This is misleading because the overall diameter of this tire mounted on a 700C 622mm rim is less than 29 inches.
The sizes written on the side of the original NanoRaptor was 622 x 52mm (or 2.1 inches wide).
So with 622mm diameter for the rim and 52mm extra for the tire you end up with an overall tire diameter of 726mm or 28.58 inches.
The tire was also marked as 17c - 29c, which denoted the minimum and maximum recommended internal rim width in mm. Even calculating for a 29mm wide rim the overall tire diameter would be in the region of 732.5mm or 28.8 inches.
So the term 29er was a marketing term based on rounding up the diameter of the tire to next size in whole inches.
The 622 x47mm Finnish Hakkapeliitta tire had an overall diameter that calculates to 716mm or 28.2 inches.
Whilst this is only 10mm (0.4") less in overall diameter than the NanoRaptor, there is a much more significant difference in the air volumes of the two tires. So whilst the 700C NanoRaptor did not actually measure 29 inches, it gave considerably more cushioning and so represented a significant improvement in terms of off-road capability.