This would have been a dealer installed option, along with painted or taped on pin stripes, which were often added to the cars (I’m sure for a nice price to the customer). Not from the factory in any year.
I have only seen them in the US on a few cars, so I don’t think they were standard on all 780s. I have a photo of the cars in the factory and I think the answer may be that those with the black turbo grill did not have them and the 780s shipped with the chrome grill, 6 cylinder model in the US. I can see models sitting next to each other in the final inspection area of the factory with both. The B230FT turbo 4 from 1989 to 1991 did not have them in the US. I’m not sure how the engine/chrome decisions were with the European models diesel etc.. Interesting to see this. I will also inquire with my contact who was at Bertone to see if he has any other information. I know my 1991 also had pin-stripes which were a dealer added “option” for sure in the day.