GIANT ON: 1969
As far as Date Paintings were concerned, On Kawara started small (size 'A' in January, 1966) but immediately got bigger ( Dates of sizes 'B', 'C', 'D' and 'E' all followed by April of 1966). He made a single size 'F' painting in that first year, on July 18, 1966, which was to commemorate the Gemini 10 space mission . 
Reproduced thanks to the understanding of the One Million Years Foundation.
Nothing of size 'F' or above was made in 1967, nor in 1968 when he moved to Mexico City and toured South America. Indeed, he reverted to size 'A' and 'B' while away from his New York studio.
Back in New York at the beginning of April, 1969, he did no preparatory work (nothing above size 'B') before launching into the three dates at size 'H' in July, 1969. It's possible he made large Dates that were destroyed because they were unfinished or not satisfactory. But on the face of it, Kawara made the aforementioned size 'F' in July of 1966 and nothing comparable until the three at size 'H' of July 1969.
There are no photographs of the Central Street studio during the painting process. Just images of the three finished canvases, which are perfect. This is what they look like when you lay the three images on top of each other and line up the characters:
Size 'F' was 41" by 56.5". Approximately 3 and a half feet by four and two-thirds feet. And size 'H' was 61 inches by 89 inches. Approximately five feet by seven and a half feet. It's possible that he used templates to produce these Date Paintings. His close friend Nobu Fukui has told me that On Kawara had a set of templates at many different sizes and that these were being used in 1967. Without permission, Nobu borrowed a template to make a Date Painting (upside down and the wrong way around) for his own birthday in June of 1967. This did not please Kawara, who effectively confiscated the Date. This also may explain why Nobu was not invited into the studio during the painting of the July size 'H' triptych.
Reproduced thanks to the understanding of the One Million Years Foundation.
Nobu Fukui might suggest that his friend used templates for size 'H' Dates. I expect he did. But we can't be sure. What we do know from 'I WENT' is that On Kawara didn't move out of his studio at all for the 24 hours that is conventionally known as July 16, 1969. In the reproduction below, I have added the red lines and made the red dot larger, since the dot is hard to see at first glance in the actual document itself. (Apologies, I got carried away.)
Reproduced and annotated with the forbearance, I hope, of the One Million Years Foundation.
Nor did the artist go out of his Central Street studio on July 20, 1969. He did make a small journey on 21 July, perhaps at the end of his marathon effort. It had always been his intention to spend the whole day watching the moon mission on television and painting his Dates. Hiroko told Lynne Tillman this in a later interview. She also said that the three paintings were not seen as a triptych at the time, which is something I'll come back to.
'I MET' tells us that only members of Kawara's inner circle gained access to the studio during the Date Painting process. Hiroko and Aoki on day one (plus a neighbour). Hiroko and Takashi Hashimoto on day two. Hiroko and Aoki again on day three. On Kawara's closest friends at the time - apart from his life-partner, Hiroko - were Aoki, Takashi Hashimoto, Nobu Fukui and Soroku Toyoshima. Nobu and Soroku were met in the days between the painting days when there was a mah jong tournament in progress amongst the Japanese-New York art community.
'I READ' consists entirely of cuttings about the moon mission. That is the case for each of the three days. Here is a sample double-page from 'I READ' , featuring cuttings from July 16 papers on the verso, and from July 20 papers on the recto.
Reproduced thanks to the understanding of the One Million Years Foundation.
And although the Date Painting itself was far too big to be stored in a cardboard box as most Date Paintings were, boxes were used to house entire copies of New York papers of the days in question. 
Reproduced thanks to the understanding of the One Million Years Foundation.
Only one box was made for JULY 16, 1969 and another one for JULY 20, 1969. But Kawara decided that two newspapers needed to be part of the documentation for JULY 21, 1969. Those would be the newspapers with images of the space walk that took place on the Sunday evening of July 20.
Reproduced thanks to the understanding of the One Million Years Foundation.
So there is no mystery whatsoever about the three size 'H' Dates on July 1969. They were to commemorate the Apollo 11 moon mission and man's first walk on the moon.
The paintings were shown together in 1993, by Dia Art Foundation, in an exhibition that showed 1000 Date paintings in batches throughout the course of a year. This may have been the first time the three large Dates were seen in a gallery.
Reproduced from the website of Dia Art Foundation.
The three Dates were shown together in a room at Dallas Art Museum in 2008. They were certainly referred to as a triptych by this time.
Reproduced from the website of Dallas Museum of Art.
Between the Dallas exhibition and his death in 2014, On Kawara assisted Glenstone Museum's efforts to build a suitable gallery to permanently house the triptych. The artist's contribution was for a layer of charcoal with therapeutic qualities to be incorporated into the ground under the wooden floorboards. This museum is about 40 miles from Washington D.C..
Reproduced thanks to the understanding of the One Million Years Foundation.
Reverting to the Dallas diagram, let me indicate where we have got to in the study of the 11 size 'H' Dates. 
Three down, seven (eight, actually) to go.
Let's try that again. Three down, seven to go. Though an eighth Date, subsequently destroyed, plays an important part in the evolving pattern.
Next essay.
