This is a great question. The answer is that the Solo Thoughts editors work to bring you a creative and informed set of titles each quarter. Sometimes, the editors will repeat a title used from the last quarter, or again in the same issue, because that title seems to highlight more than one Bible Lesson in an important way.
Conversely, in order to highlight new music and new composers whenever possible, the editors may sacrifice listing titles that were recently used in a previous or current quarter of Solo Thoughts. On the whole, WFM and the Solo Thoughts editors feel that it is very important to bring new musical ideas for Bible Lessons and to introduce new titles wherever appropriate and possible.
Tip: Hang on to your Solo Thoughts from previous quarters in a given year and perhaps make notes on solos that you think would work well for future Bible Lessons.