0
Shouldve is the key term.
I always found it odd that they went on to portray John Shepherd as merely a year or afew years older than what the character was in Part 4. That said, I think Part 6 nailed it right on as its not clear how long Jarvis was in an institution except for several years have passed between Part 6 and Part 4 and if you debate it with the experts on the series. Some lean one way or the other on whether or not Part 6 does or doesnt ignore Part 5.