Yes, you should follow Erika's advice.
Using Subset a.k.a Migration libraries isn't a migration nirvana but they provide two very important advantages.
First of all, you can access all previous and new elements in your projects without an error-prone duplicatied-element-situation. Second, migration libraries are 'finalized' to the latest ArchiCAD so for example Migtation Library 11 is faster in AC12 than the original ArchiCAD Library 11.
If you encounter any problems using the migration libraries, please let us know.
Regards,
Zsolt
Zsolt Táskai
ArchiCAD Development - GDL Team
AC13, AC14 and upwards...