Those previous "non-annoucements" weren't connected with a major anniversary date. Nor, if I remember correctly, did they come with a splashy "Coming Soon" web page with zero details.
The D5 pre-announcement was very much alike, with very little detail, only that they're working on it, and it supports a new type of wireless flash. The D5 was announced at a trade show but more importantly the real deadline was the Rio Olympics.
Nor is it true that Nikon launches "when everything is ready," unless you think it's coincidence that so many Nikon announcements take place at major trade shows.
Actually Nikon seems to launch stuff pretty randomly through the year and the announcements usually do not coincide with trade shows. Nikon announced 105/1.4 some time before Photokina and 70-200/2.8 and 19mm PC just after it. Customers get their information from the internet these days, not at trade shows. The 8-15mm, 28/1.4, 10-24, 70-300 AF-P, D7500, also announced not at any trade show I'm aware of. Of course it's possible that there was some trade show in some country I never heard about but the thing is that trade shows no longer have much impact on annoucement of products for Nikon. Or Canon for that matter.
But marketing opportunities like a 100th anniversary don't come around very often. Nor do they exactly come as a surprise. Especially after the DL debacle, Nikon needs all the good press and it can get.
I would be suspicious if a major product was launched at a 100yr birthday. It would indicate that either a) Nikon may be rushing things to meet a calendar deadline, which is never a good thing, or b) they've been holding up a product that has been ready for a while just to announce it at a birthday that occurs every 100 years (losing money not selling it while the product is at its most relevant). I think random announcements throughout the year is the healthiest sign because it shows that they are launching products on their own terms and do not let external pressure influence the launch.
