I think that there should be an alert for a base being locks and an alert for a base being disabled apparent to players to hit it.

For example.

Players A, B and C are online, D and E are offline

Player A Locks Base
Players B and C receive an alert that Player A locked a base (Like with NPCs)
Player A and B hit the base
Player D comes online and receives an alert that Player A locked a base (Like with NPCs)
Player D disables the base
Players A, B and D receive an alert that the base has been disabled (Like with NPCs)
Player C ignored the base so gets no alert of the disable (Like with NPCs)
Player E comes online and receives no alerts (Like with NPCs)

All players would still have the alert recorded on their ship log, regardless of whether the red box alert showed up for them. Like with NPCs.

In other words, you propose leaving the system working exactly as it is currently working, but change the notice that goes into the legion com to be the announcement style notice, so that Leaders don;t do that themselves.

Note: NPC alerts will still show to player E when he comes online even though the NPC was disabled before he came on, so long as they are within a certain time frame. Also Note: NPC alerts for NPCs that are over that certain time frame would not alert player D when he comes on if that time frame has come and gone. (--That is to say, NPC alerts do not actually function as you describe them above. --)