I dug up an Estes publication ("The Classic Collection") which has a
copy of TN-1 in it. It shows a thrust curve for the A8 that matches that
for the B4 except for that long tail. Peak thrust of about 13N and all
done in 0.3 seconds.
So it is possible that they really were made that way. The B4 would just
be an A8 with extra BP for some end burning action.
When and why that changed I have no idea. The test data on the NAR web
site says it was collected in 1995 so sometime before then.