I have several shared neutral circuits in my house (built in CT approx 1980) that do not have ties between the breakers to ensure that both are turned off together. I'm not 100% positive that they are all adjacent (it would take some time to determine exactly which circuits are set up this way). I assume this was to code when it was built and inspected, but I understand current code requires tieing the breakers together.

My question is whether I should go to the effort and/or expense to retrofit tied breakers.