When FCBIS runs there are several partial states 2-phase index builds may be in.

1) Index build has started in checkpoint but not completed (no oplog entries)

2) Index build has started in checkpoint and completes in recovery (commitIndexBuild only)

3) Index build starts in recovery but does not finish (startIndexBuild only)

4) Index build starts and ends in recovery (startIndexBuild + commitIndexBuild)

Currently FCBIS handles only cases 1 and 4 correctly.