Basically doesn't matter unless you are showing pigs.
Legally pigs do not need any individual ID.
So if you are doing say meat pigs, and tagging just before slaughter, then no point in having individual no.s
However some people tag for management purposes and tag their litters eg to be able to say that no;6 was off its food this morning.
If you get into showing, then indiv ID tags can be used for this purpose.
Many on-line manufactures offer numbers as standard - so just go for any number you like, or leave blank, the key is that the tag has you herd no. (one or two letters, 4 numbers) on it.