I never heard that before. The Haynes "Weber Carburetor Manual", which also includes SU and Stromberg data, only lists one B1AF needle. If the profile was changed they would have used another letter/number designation.
Heres a comparison with the B2Y used in the TR250 and 69 TR6:
Stromberg Biased Needle
/ubbthreads/images/graemlins/hammer.gif B1AF B2Y
1 .0951 0.0967
2 0.0942 0.0932
3 0.0923 0.0905
4 0.0897 0.088
5 0.0864 0.0848
6 0.0835 0.0816
7 0.0798 0.0779
8 0.0771 0.0755
9 0.0749 0.0735
10 0.0731 0.0715
11 0.0712 0.0695
12 0.0695 0.0677
13 0.0695 0.0677
The whole numbers under the hammer are stations, which refer to needle diameter measurements taken every 1/8th inch, starting with Station 1 at the shank. The smaller the diameter, the richer the needle at any given station.
In the above comparison the B2Y is leaner at idle, but then richer at every point in the range thereafter.