For example,
* XYZ has 1 year of work experience before.
* He/she gets hired at a company into a junior position, which does not require any work experience. All is well.
* Two years later, XYZ gets promoted to a senior position (after new H1-B approval). The senior position has a minimum work experience requirement of 2 years.
XYZ is fully qualified for the senior position since he/she has now 3 years of work experience, one of which was gained prior to joining the company, and 2 gained at the company in a junior position. However, for PERM purposes, the 2 years gained at the same company cannot be counted as qualified experience.
This is why PERM is not user friendly for those with little work experience. The drawback is on two fronts:
(1) with little work experience, the person probably has to apply for a EB1 green card, which takes forever,
(2) even when promoted, experience gained at the same company cannot be counted!!
This is just my understanding and anyone who knows better please clarify/correct.