Hi Bill... aquesta és pregunta d'examen, eh! :)) Well, "technically" the city only has 10 districts divided in 73 neighbourhoods.... period.
However, there are still indeed some other unofficial "names" used by the longtime residents of certain areas of the city. This is mainly due to the historical evolution of the administrative divisions of the past. Over the centuries, the city has been divided over and over into different "areas" as it grew and expanded. Also, when absorbing the neighbouring villages and towns in the plain of the current city, names were changed. Note that current places like Poblenou, Sarrià or Gràcia were independent towns until fairly recently (the last merging took place between 1897 and 1921)
Once can still find street plaques showing this evolution, especially in the Old City, ie this one -from the era when the Spanish didn't allow us to use our mother tongue and local language, Catalan, and everything had to be labelled in Spanish. In the era of this particular plaque -probably late 1800s-, subdivisions were referred in numbers as you can see in the image.
Anyway... summarizing, yes, some of us locals use certain names to refer to certain areas, but they're not official --either they are no longer official or they never were but popular use made them... popular. In any case, for visitors' sake, I think it's best to stick to the official denominations in order not to confuse them since the unofficial names are not to be found in any website/publication. Just my opinion, of course.
Btw Bill... if you were to say to me to meet in Sant Roc I would probably think you're referring to the neighbourhood of BADALONA -to the north of Barcelona, for those not familiar- and would likely think to myself: "WTF!" because it's not precisely a "nice" neighbourhood to wander, LOL!
PS: Yes, yes, I know you're referring to the extinct Sant Roc "neighbourhood" in the Old City in Barcelona, haha! The Festival of Sant Roc, for those visiting in mid-August is, of course, a must. You'll see a lot of a typical Catalan Festa Major bits there. And it's free, of course.