Delphi 1 was a mess. Delphi 2 was rock solid. Delphi 3 was a buggy mess. Delphi 4 kind of recovered things but was never as good as Delphi 2. By this point we'd figured out the pattern and skipped Delphi 5, if I recall correctly.
1 was 16 bits only. 2 turn to 32 bits AFAIK.