Question

1. I had a book.
2. I'd a book.

3. You had a pen.
4. You'd a pen.

5. He had a car.
6. He'd a car.

7. We had many pens.
8. We'd many pens.
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Are the contracted forms all grammatical?

Answer 1

Nope. None of them are.

Answer 2

For these contraction forms to be correct, you need to use them only when "had" is an auxiliary or helping verb.

I had a book. ("had" is the main verb and is not to be contracted)

I'd been staying at her house until I found my own place. ("had" is an auxiliary verb with "been" and thus can be used in contracted form)