@YorkshireFelix Pupsy never used to bark either and I reckon she was probably about V’s age when she started, so I wonder if it’s partly hormones.
She doesn’t bark at the door or when people go away from her (as she invariably comes with anyway) but she does bark a bit during meals, though she’s getting much better. My response depends on why she's barking. When she barks during human mealtimes it's most likely because she's attention-seeking, as if I’m eating she’s got/has had her own meal. In that situation I stonewall her and don’t give her any attention whatsoever, and it tends to shut her up after about four woofs when she realises it isn’t working. Conversely, if she barks at the dark garden when she has her last wee it’s probably because she’s suspicious of something so I give her a fuss when she comes in.
I think in your position I’d ignore any kind of bratty barking, like when you were upstairs and he was downstairs. Just literally no response as even a firm ‘no’ or ‘quiet’ gives them attention and it’s attention they want, whatever form it takes, but I appreciate that you don't want to disturb your neighbours which is an added element. He shouldn’t have any reason to be worried about you going upstairs, especially if someone else is downstairs, so to me that’s just him being annoying and it doesn’t deserve any attention.
But each situation is different. I wonder if the barking last night that required a remote control to settle meant that he was overtired? He’s bigger, but he’s still a baby and I think sometimes they still need helping to sleep – or confirmation that it’s time to settle down now – and bark to let us know. That’s my theory based on what pupsy does as occasionally in the evenings she will woof at me when I’m on the sofa when I know for sure that she needs absolutely nothing from me except to sleep on my knee.
You have my sympathies as I know how annoying it is but like with most dog things I just don't pander to it as then they learn that barking gets a response.