Sorry for making you feel uncomfortable by asking about the date you posted. Please don’t feel bad for any mistakes like that. We are happy you choose to post here and make the effort to use a translator.
You were correct in your post saying the 5th anniversary started earlier in the month than the 6th anniversary. Here are all the anniversary eggs…
1st anniversary: 1 egg (Penguinator)
2nd anniversary: 1 egg (Delugazar & Mojinator)
3rd anniversary: 1 egg (Nulltron & Novadrake) + Halloween egg (Maggatsuoh & Pumpking)
4th anniversary: 1 egg (Don Rilla, Pandamonium & Whitetitan) + Halloween egg (Scyberithe, Scorpiogeist & Blacktitan)
5th anniversary: 2 eggs (Cynthia, Padrinorca & Lordstag // Fiona, Razorstorm & Leomidas) + Halloween egg (Kirina, Jack-o’-scorp & Vinegazer)
6th anniversary: 2 eggs (Vixian & G.F. Hibi // Wilhelmina & Dolphoone)
7th anniversary: 2 eggs (Apollonis & Ldiefaeth // Gabrielle & Rexterminator)
8th anniversary: 2 eggs (Honghua & Strawbaba // Charybdia & Trimaegus)
So the 5th anniversary was the only time they had 3 eggs. They decided this was too much. You can see what happened was they added a Halloween egg for the 3rd and 4th anniversaries but then wanted to do 2 eggs for the anniversary so they did all three then decided for future anniversaries they wouldn’t do a Halloween egg. Every year the 1st of the anniversary eggs starts on the week of the anniversary (22nd Oct) except the 5th anniversary where it started one week earlier (to line up the 3rd with Halloween properly).