To my knowledge most Artists produce more than one version of a successful painting. Monets Haystacks and Van Goghs Sunflowers.
I get offers to do Comissions occasionally and a picture for guidance is referred too . It can be a blessing and a curse.
A blessing because it spurs you on to a new challenge and is much needed cash and a curse because it can interfere with what you are currently doing and put you on a back foot when you return. It can really interfere with the natural flow. Or on the other hand if things are not flowing it can be a pointer.
So far I have found them useful and I seem to learn and have managed to thrive with the dilemma and enjoy the challenge.