maintain internal number ranges at spro > logistic general > material master > basic settings > material type > define number ranges for each material type. It is possible to maintain one internal and one external number ranges for a material type.
but material types should be maintained in groups because number ranges assigned to groups.
if you want separate number range for each material type maintain each material type in seperate group
Check What I found and hope this will help you,
Go to MMNR and Press Ctrl F and type Not assigned It will show you the Not Assigned Group in that Check Whether your Material type is there. If its there, Look for other Number range groups other than Not assigned then Select your Material Type and Click on Element /group icon and save.
Identify your Material type in Not Assigned groups
Select Other Material Number assigned Group
Click on your Material type
And Click on Element/group and save.