According to the Economic Development Corporation of Los Angeles Count

There are three types of conditional sentences: First Conditional, Second Conditional, and Third Conditional

1. First Conditional: if clause = If + present tense, then main clause=- future (will) or present tense + bare infinitive
(Bare infinitive means the base form of the verb)
Example: If I have enough money, I will buy a house (future tense)
If the sum of the digits of a number is divisible by three, the number is divisible by three

2. Second Conditional: If clause = if + simple past tense, then main clause = would or might or could + bare infinitive
Example: If I had enough money, I would buy a house
If I were Bill Gates, I would donate $100 to Mother Theresa's Ashram every month.

3. Third Conditional: If clause = If + past perfect, then the main clause = would have + past participle (technically called the conditional perfect)
Example: If I had had enough money, I would have bought a house.

rishabhdxt wrote



The 'would have' in the then clause you have referred is not past perfect. It is simply the future past of will namely 'would' + the bare infinitive 'have'. This example corresponds to the second conditional cited above.
If you want to use a past perfect in the 'if clause', then the sentence will be:

if one had counted the Los Angeles metropolitan area as a separate nation, it would have had the world’s eleventh largest gross national product -- Please note that the conditional past perfect you had in mind takes the form of 'would have had'