Is there any problem if domestic and export sale invoices numbered in same series?

We have trading business, we make domestic sales and now also started export (outside India) sales.

Currently we are numbering domestic sales invoices as '1', '2', '3', '4', '5',...

My question is can we generate export invoice and domestic invoice in same series, or should we start a seperate series for export invoices like this (Exp-1, Exp-2,...)?

Please advice, thanks in advance.