It would seem reading the letter literally.
But when taken in conjunction with this:
It would seem he was always referring to the 1st moon "walk"
Also inferred is Omega only really only wanted to confirm
"the first"
http://www.chronomaddox.com/moonmovement.html
We have TZ Classic 381 in which John Diethelm of Omega Vintage Information is quoted as stating:
"Dear Sir,
In reply to your net inquiry dated febr. 19,1999 here are some details:
1. it is obvious that the first moon landing was made with a Speedmaster fitted with a caliber 321 movement. The toward the seventies, the NASA has probably also used the replacement movement caliber 861. We have no official confirmation of what has been used and when, except for the first Moon landing.
2. The re-qualification in 1978 is exclusively made with the caliber 861."
Kind regards
OMEGA LTD John Diethelm
Note: This is not necessarily true, because we do have the photo's above and additional pertinent information below. But, I present it as is nonetheless.