Serial No for multiple units

Have a look at the following,

"GST Registration by Type of Taxable Person

• Every person has to apply for registration in every State in which he is liable, within thirty days from the date on which he becomes liable to registration.
• Casual/ non-residents should apply at least five days before their commencement of business.
• Registration number in GST will be PAN based and hence, having PAN would be a prerequisite for obtaining registration.
• The assessee must obtain separate registration for each State, as registration under GST will be State-wise,
• The assessee has an option to obtain a separate registration for each of the ‘business vertical’ in the same State."

Now you may get your answer that you have a choice if all the Units are within 1 state then you may opt for separate registrations or single registration.