The thirtieth of February?

[TheGreatElvenWarrior]

In the Appendix B of LotR where The Tale of Years are and the Great Years start, under February it says

29 Meriadoc and Pippin escape and meet Treebeard. The Rohirrim attack at sunrise and destroy the Orcs. Frodo descends from Emyn Muil and meets Gollum. Faramir sees the funeral boat of Boromir.
30 Entmoot begins. Eomer returning to Edoras meets Aragorn

It also states in the Shire calender, the second month out of the year, Solmath has thirty days, but that is the Shire calender and it differs from ours.
This has gotten me confused, is this "February" that is stated in Appendix B the 'Shire February' or 'our' February, because if it is our February, then it should have only twenty eight days and twenty nine if it was a leap year, how then does February have thirty days? Is this just a typographical error that Tolkien and his publishers made, or was this 'error' supposed to be there and I am missing something?