This type of situation is not specifically addressed in EBAE. We know that the print reads ABC and that's double capped. The letters that follow the number have nothing to do with the letters at the beginning. The number sign has terminated the caps in order to institute numbers, so the only question is whether numbers are continuing or changing into letters. In this case, there are letters following numbers so, you would need the letter indicator to indicate you are going from numbers to letters. If the letters after the numbers were also double capped, the double caps would have to be used again after the letter sign.
To answer your question, I think the number sign terminates the double caps ABC. And the letter sign after the number terminates the number.
Hope this helps.