GST Invoice number format question on random part

I have a question about generating GST invoice numbers. I have read the exact rule:

a consecutive serial number not exceeding sixteen characters, in one or multiple series, containing alphabets or numerals or special characters- hyphen or dash and slash symbolised as "-'' and "/" respectively, and any combination thereof, unique for a financial year;

But I am not clear on what they mean by multiple series. My account s/w generates sequential invoice numbers but the middle part of the invoice number is random (so that no one can guess the next invoice number). For example, the 15th invoice is 20230727-WXYZ-15 and the 16th is 20230727-AMNO-16. So you see 15, 16 is consecutive but the middle part is random. Is that valid for uploading GST invoices?