This rumour seems fake anyway, from what I've understood the first number is supposed to indicate whether the card is high/mid/low-end and there is supposed to be a letter before the three numbers, as in:
7990's successor would be named R9-D290
7970's successor R9-D270
7950's successor R9-D250
7870's successor R8-D270
8970m's successor R9-M270
Something along those lines. Otherwise the "9" would be entirely irrelevant.