Maybe Libby, Boone and Charlie's death were the easiest for the O6 to lie about in a consistent way without having to worry over messing things up? Eko's death, not all the O6 people know as to why and how. Ana Lucia wasn't everyone's favorite, Shannon didn't really have anyone off the island who would wonder or question what happened to her..

Mentioning Charlie on the other hand would keep the press busy for some time (death of a semi-celebrity, shocking news recycled for DriveShaft fans) while it could also mean a way to honor his memory. He couldn't get a proper burial so the least they could do is verbal closure.

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"Bear...? Is that you?"-- Hurley S03E4