If you want 49 counters, you will need 49 counters. You can probably program something as smart that will create a number based on where in PDM you are, but that is not out of the box.
49 separate templates with their corresponding serial number counters.....
Luckily you can create the first one, then copy it and make mods to it.
I would make an add-in that monitors adding files to the vault. When a new file is created, the name of the directory with the highest number+1 of the file names will be combined. Afterwards the file will be renamed. In this way, any number ranges can be managed, no matter how many of them will be in the future.