Extension concept in D365FO

Dear All,

Can you please let me know say I have created a new model "ABC" and add elements in base enum say NumSeqModule.my extension.

Here I am creating a extension because going to add new elements on standard objects.

Say for example I added new elements "Test".

My question is if anybody going to add new elements again on the object "NumSeqModule.my extension" then he should work on the same model "ABC" only then only he/she can add new elements on NumSeqModule.my extension.

If they creating a new model say "ABC2" and trying to add new elements on  "NumSeqModule.my extension" then it will not allow to do  they need to create a new Extension for NumSeqModule for this new model. Then only they can add new elements.

Is't correct?

Please give me more shed on this.

Thanks!