So far the PLAN seems to have a rule of pennant numbers like this:
1xx, destroyers
5xx, frigates
4xx, nuclear subs
We have also seen CVs with 16 and 17, LHA 31. It looks to me it is a pattern that PLAN decided to have two digits for CV and LHAs or anything that is significantly large in size and role.
This leads me to think that 1x and maybe 2x are reserved for CV if we follow PLAN's tradition. This means that there won't be anything from 1 to 9 (0x series). However, it does not explain why they skipped 10 to 15.