A name kept off the announcement can still belong to someone who made the result possible.

Credit lists are shorter than the work. Announcements name whoever presented, signed or led, while the person who found the error, kept the schedule honest or did the tedious middle stage often does not appear at all. Absence from the list is not evidence about a contribution, only about how lists get made. Most results have more parents than the notice admits.

If you are writing the announcement, add the two names nobody would think to include. If you are not, thank someone directly whose part went unrecorded. Being seen by one person who knows what you did carries further than a public list.