I finally got some time to dive into it and with the great speed of Neko, it was a lot of fun to get more insights from this data. I decided to publish my results openly, so anyone can use it for his own purpose. I would be interested to develop a web/mobile app out of those data, do not hesitate to contact me if you would like to commission something like that.
The sightings are grouped by week. Therefor, when you read 1999.1, you are referring to the week number 10 from the year 1999 (the week number 1 would be 1999.01).
To highlight the main events, I kept only the weeks that contain at least 25 reports.
For each of those events, I also saved a text file with the detail from the sightings per shape. I only saved it when the shape was reported at least 4 times.
In order to get more relevance with the shapes being reported I grouped them as following: