Mongoose Validators
According to Mongoose Validation docs, you can run validators when updating you data, but you must explicitly tell Mongoose to run them.
This is a quote from the Update Validators section taken from the link above:
Mongoose also supports validation for update() and findOneAndUpdate() operations. In Mongoose 4.x, update validators are off by default - you need to specify the runValidators option.
To turn on update validators, set the runValidators option for update() or findOneAndUpdate(). Be careful: update validators are off by default because they have several caveats.