An interesting detail is that after the first four 054A the list calls them 054A II. That corresponds to another source calling Hulls 5 and later the 054A+. If there has been a (not visible) design modification, it would go some way to explain the two-year pause between Hulls 3-4 and Hulls 5-6.
There is some visible design modification. The type 054A+ or 054A II have improved and straighter bow shape.
type 054:
type 054A:
so called 054A+: