Separating styles of numbers for simple digit classification
Interesting question. You are right in assuming that some 1s may be confused for 7s, same with 8s and 3s for instance.
Generally creating different classes as you suggest doesn't happen, simply because it would require more annotation.
There are multiple ways to handle this.

stacked models

Anything labelled as a 1 or a 7 would be given to a model fine-tuned to differentiate these two specific digits

weighted training

It is possible to teach your model that some mistakes are worse than others. In your case, 1s for 7s is bad, so you could increase the cost of making that mistake.