codes: They do seem to waffle on the Interim title.
As of 8/18, Robert was still Interim Chief Financial Officer. As of 8/12, Laura was Acting Cheif Executive Officer. Interesting, both upper case and lower case "Acting." As of 8/12, George is "acting Chief Operating Officer" only lower case.
The modifier "acting" applies when the executive post is filled on a permanent basis, yet the permanent appointee is unavailable, e.g. because of extended travel, sabbatical leave, or illness. The modifier "interim" is used when the executive post is vacant. In other words, an acting officer serves in the absence of a permanent appointee, but an interim officer serves through a period between permanent appointees.
Considering they do have a permanent HR person, I assume the terms are used correctly - except for the upper/lower uncertainity.