It was not the intention of the Lutheran Service Book to commemorate the birthdays of Martin Chemnitz and Philipp Melanchthon. It is rather these two reformers who are commemorated. They are remembered on their earthly birthdays (9 November and 16 February, respectively), instead of their heavenly birthdays (when they departed from this life on earth), primarily because the Church has generally tended to avoid commemorations during Lent and within the Octave of Easter.
This year, and at other times when Easter is early, the 16th of February does occur within Lententide, but that is usually not the case. However, Chemnitz died on the 8th of April, Melanchthon on the 19th of April, and those dates frequently do coincide with the end of Lent or the beginning of Easter. In addition, the sanctoral cycle in the Lutheran Service Book was developed with the Treasury of Daily Prayer in view, for which those commemorations within the movable Time of Easter are far more difficult to connect to the daily readings and other propers.
Because Chemnitz and Melanchthon are too important to be overlooked or forgotten, and there was precedent for remembering these men on their earthly birthdays in the old Lutheran Annuals, those dates were chosen for the LSB. Regrettably, the parenthetical notes identifying these dates with their births was retained and actually published in the hymnal, although those notes were only intended as a point of information for the committee as it was working through the data and proposals. There was no desire to hide the connection to the birthdays, but neither was there any intention of commemorating the birthdays per se.
It is typical to remember the saints on the date of their departure from this earth, but that is not always the case. In other recent calendars, for example, Melancthon is commemorated, not on the date of his earthly death, but in connection with the Presentation of the Augsburg Confession on the 25th of June; whereas Chemnitz is simply not included.
It is a beneficial coincidence that, with these dates in LSB, the commemoration of Philipp Melanchthon occurs in close proximity to Luther’s (on the 18th of February); whereas the commemoration of Martin Chemnitz occurs shortly after Reformation Day (31 October) and a day before Luther’s birthday, which most Lutherans have been more familiar with. Both Luther and Chemnitz were named for St. Martin of Tours, who is commemorated on November the 11th.