Mine is one of them and I asked Norm Miller the same question.
Here is his reply.
I'm sure won't mind me posting it.
It's actually pretty simple. I'm not sure many know there was an
axle shaft upgrade to the DANA 44 during Tiger production. The
Jensen scribes dutifully chronicled the introduction of those
improved differentials. At some point all of the supplied back axles
were second generation units, so the "Special Axle" notation was no
longer necessary.
