Just solved the 1AC mystery of VRL - BCT. Involved research, but paid off.
There are 3 cabins in this train in 1AC (part of HA1 - which also has 2AC) - One 4 berth and Two Coupes - total of 8 berths.
This train joins Saurashtra Mail at Rajkot and therefore, the quota system kicks in. Only 2 1AC berths are avbl from VRL to BCT. That's why the availability always showed '2' 1AC berths.
But...
more... the quota VRL to RJT is 8 berths and RJT to BCT is 6 berths.
So I did the workaround - separately booked VRL to RJT and RJT to BCT. Got confirmations for 4 berths - which means that I will get the same cabin - for the full journey.
Phew!