Anything special is required to raise population in the Sanctuary? At first there was 6 of them. At the very moment, I activated recruitment signal, 7th showed up, and that's it.

I have more, than enough beds (16), food (12 + more awaiting for the farmers), water (16), power (20), 80% happiness, shops waiting for anyone interested, defences (42) and 6 of Charisma...

Many in-game days later, after about 36 hours of gameplay, there's no any change, while in the meantime population of the second, tiny and much worse equipped settlement, that started later, was raised from 2 to 10... Is the population of Sanctuary growth bounded somehow with Minutemen quest?

I have the strategy guide and it says that the population is based on your charisma level. I have a charisma of 6 or 7 (whatever the requirement for local leader is) and my max population is 15

Yes, my limit should be 16 then. It's all the time 7 though (6 of initial Minutemen group + 1 added just after activating recruitment). Nothing changed since then. In the other, much smaller settlement, all 10 beds was filled pretty fast in the meantime. So either I'm very unawared about something, or there's a glitch blocking population growth in Sanctuary for me.

Not sure, got mine to 11. I think settlements are a tad buggy. Some of my stuff gets damaged for no reason I can figure. Like at one point, I went from producing 120ish water to 0. No notice of my settlement being attacked. (At least that I saw). I am pretty sure that slowed my population growth down.

I think that your companions have to also count towards the limit as well. Ditto on any one that you send out as a provisioner..

Mine's been stuck at 16 since like the third day the game was out. Other settlements are 18 - 19, but sanctuary is stuck.

Well, I'm roaming with Piper, Dogmeat was sent away, two other offered their company. Even counting all of them, which makes no much sense, it's still 11 (displayed number is 7 though) - The provisioner for the Sanctuary is this 7th guy, the only, I could point for this task, all the rest are "untouchable" and can't be assigned for this job.

I have a corollary question: If a particular settlement is at maximum, what happens when we try to send a named NPC we've recruited to that settlement, such as the alcoholic from Diamond City? Does he displace an unnamed settler, or is he just unable to go?

Being particularly retentive, I want to assign all of my settlers at Sanctuary individually. I'd hate to have that mucked up if I send someone I meet in the Commonwealth there. (I also personally prefer named characters to generic "settlers.")

Has anyone come across this to know what happens?

The settlement named is blacked out on the list and ou are unable to send him there.

Also, you are unable to start a caravan from a different settlement to the maxed one, since that counts as sending someone to that settlement, but you are able to send someone from a maxed settlement to a non-maxed one.

Thanks so much for the reply, Possum!

In my experience, it just takes FOREVER to get settlers in sanctuary compared to other settlements

Perhaps that's the case. Still no new settlers, but I sent there Piper and the beggar from Crystal City, so there is count of 9 currently.