Since it is clear you won't taken anything less as proof, despite the numerous other sources given by myself and others, I put way too much work into this today to finally put this issue to rest.
For starters, the most recent generic giraffe SSP plan contains a graph showing each founder of the population, a total of 96 founders. With this information, I used CTRL+F to find each of the 96 founders as quickly as possible in the 2011 studbook you provided. Out of 96 founders, 87 of them are listed as subspecies "ret/roth". Unfortunately, each of these 87 founders had their location of origin listed as either Kenya or East Africa, and given that multiple species of giraffe live in each of these locations, it would be impossible using the studbook to determine the actual identity of any of these individuals.
That leaves us with a total of nine individuals that are not listed as "ret/roth" to analyze the descendants of. Out of these nine individuals, one of them (SB#409) is listed as a "hybrid" and one of them (SB#206) is listed as tippelskirchi. Since the Masai giraffe population is managed separately and isn't part of the genetic question, that individual would not provide any additionally helpful insight to this study.
Of the seven individuals remaining, three (sub)species of giraffe are represented: reticulata (SB# 207, 474), camelopardalis (95, 96), and rothschildi (5-336, 5-339, 5-337). With this information in hand, I will now go through each of these individuals to determine if any had offspring together that would be of known pure subspecies.
Reticulata
Two individuals were listed as subspecies reticulata. One of them was a male giraffe who lived at the Dallas Zoo from 1956-1978, and the other was a female giraffe who lived at the Cheyenne Mountain Zoo from 1968-1995. Given that there were no offspring between these two individuals, there are no individuals based on the information available that can be proven as pure reticulated giraffes.
Camelopardalis
These two individuals, 95 and 96, were both imported from Sudan to the National Zoo in 1937, where they lived until their deaths in the late 1950's. There were offspring from this pair, including a daughter who was back-bred with the father. However, the last individual in the studbook I could find who was descended purely from these two founders was a female that died at the Honolulu Zoo in 1985. Given that all the other founders were listed as "retic/roth", it is all but a certainty there are no purebred giraffes of this species in US zoos, although some of this species' genes are still floating around in the generic population.
Rothschildi
These three founders (5-3336, 5-3339, and 5-3337) were the parents to three giraffes imported from Woburn, England to the African Lion Safari in Canada in the 1973. This trio of giraffes had three offspring. Two of them were later exported to a zoo in New Zealand, while the third went to Zoo Granby, where she lived until 2005. There are no individuals left alive descended purely from these three founders.
Basically, your idea that we can find purebred individuals in the 2011 studbook is completely false. Unless you or anyone has information on any of the 87 founders listed as "ret/roth", then the closest I can get is that the last confirmed purebred Northern giraffe died in 1985, the last confirmed purebred reticulated giraffe died in 1995, and the last confirmed purebred Rothschild's giraffe died in 2005. I see no reasonable way to not believe those of us stating there aren't purebred individuals in US zoos, and that they should all be changed to generic in ZTL.
