"as early as", e.g., as early as 2000...?

Solution 1:

It will depend on the context. In a chronological narrative you would use simple past. e.g.

In 1999 the first X came out. As early as 2000 XXX was developed. In 2001 developers discovered a new method. etc.

If however a development in the year 2000 is being contrasted with an event or events that happend later but still in the past -- i.e the main time reference is after 2000 -- then you would usually use the past perfect.

In 2017 X came out, but as early as 2000 XXX had been developed.

This is not strictly dependent on the phrase 'as early as 2000'. It would be the same situation if you had written 'in 2000'.