The B1 entered service in 1956. Along the way they had upgrades to produce the B1A. These had different wings(?), electronic counter measures and capability of in-flight refuelling and uprated engines.
In 1960 the B2 entered service with all the changes the B1A had plus different, more powerful engines and lots of detail differences to accommodate them. They also had a great deal of radio and nav equipment updates.
As Soviet missile and fighter development advanced the Vulcan's operational profile was changed in the mid-sixties to a low level attack and B2 airframes were strengthened to reflect this.
As our primary nuclear deterent was about to change to submarine launched Polaris missiles it was judged not cost effective to upgrade B1 aircraft to low level work and they were all withdrawn by the late sixties.
When I was at school we had a maths teacher who had been a v-bomber navigator in the RAF and he could occasionally be persuaded to talk about it.
For all bomber crews, whether they were British, American or Soviet, nuclear war was a one way trip. No one had the range to return home after bombing their enemies major cities.
The Vulcan's fuel use at extreme ranges in combat use was apparently a bit of a mystery and it was generally accepted that the Vulcan force would run out of juice somewhere over western Poland or East Germany on the way back.
There was some debate over whether they'd get a better reception from the Poles or the Stasi....