Number Range Question in CRM

Hi ,

I have a question on number  ranges in CRM .

We have a scenario where Internal Number Range is set between : 400000-500000

And External Number  Range as :  370000-399999

Now if the external number range have been already consumed with say with 100 Orders , can we change the external number range ? Or how do I make sure that the external number  range is consumed ( as I dont see current number in external number range )

Please do let me know your thoughts on the same

Regards

Vinayak