Kolkata VAC - Dropbox option

Hi All, Kindly assist me on below query:

I have got H1B VISA Stamping appointment next week in Kolkata VAC. As, I am eligible for Dropbox option, I thought I can submit my docs in my current location - Bengaluru VFS center itself.

But, I got the info that, Bengaluru option is available, only if would have booked appointment in Chennai VAC. When it comes to appointments in Kolkata VAC, the only option is to directly visit that VAC itself for submitting docs…

Is it true ??