Short of pulling a few out along the row there is not really any other way.

Sometimes the foliage will 'pale' but this could be a feeding problem too.

Consider it to be a similar task to thinning out!

If what you do pull out are a bit small you can still consider eating them and leave the remainder to develop!

Last year ( or should that be ths year) I was still pulling them after Xmas as I always think leaving them in the ground is the best form of storage!

You could scape a little soil away from the top of the carrot to see if the root has fattened up.

I did think of that Bulba, but with so many types of carrot on the market the tops could give a false impression, plus if they haven't been thinned( like mine) you can't see the tops for foliage:o))