Last summer, I sowed Swiss chard (Bright Lights Rainbow Chard) and kept it overwinter. It lasted fine but began to bolt in the late spring.
However, I read somewhere that chard could be perennial, so rather than rip it out, I decided to keep it and see what happened.
The long and short of the situation is that there were no spectacular leaves over the summer. On the other hand, it does now seem to be producing something, though the plant looks nothing like the one you’d normally expect after sowing.