I ask, because I have 11 supply lines leaving/coming from/to Starlight Drive-In, but I incorrectly had the fort go to Sanctuary (don't ask me why I did that, because I don't know). I tried to reassign the settler doing that route, and the game would show me any other settlement to reassign him to, OTHER than Starlight. I intercepted him at the Fort, went into build mode, assign yo supply line, and Starlight was not listed. So I intercepted him at Sanctuary instead and it was exactly the same thing.
Is 11 the cap (seems like a weird number)?
Or is this a bug?