STUMPERS LXXXVII

This Stumper has two versions:

Harder version:

What two letters are missing in this familiar sequence?

MA MJ ?? SO ND JF

Easier version:

What two letters are missing in this familiar sequence?

JF MA MJ ?? SO ND

HINT:
Notice that there are twelve letters.

Answer:

The letters are the initial letters of the twelve months of the year. The missing letters are JA - for July and August. The first version is harder because the sequence begins with March/April, instead of the usual January/February, as in the second version.