[Grammar] tense used with since

[mrachidi]

Hello,

I am wondering which tense should I use in this sentence! Could you please tell me also the reason behind it?

Since December 2014, the Bank’s headquarter is located in Paris.

The Bank’s headquarter is located in Paris and has been since December 2014.

 

[emsr2d2]

Since December 2014, the bank's headquarters have been [located] in Paris.
The bank's headquarters are in Paris and have been since December 2014.

You will notice that I have used "headquarters" and followed it with the plural. There is a BrE vs AmE here. I understand from one of our AmE members that it's "headquarter" + singular in AmE.
In BrE, even if it's just one building, we still use "headquarters" + plural.

 

[MikeNewYork]

This AmE speaker uses "headquarters".

 

[Tarheel]

This AmE speaker would say:

The bank's headquarters is located in Paris and has been since December 2014.

 

[emsr2d2]

Ah, that's interesting. I hadn't seen an example of "headquarters + is" on the forum before.