as I didn't

[azz]

a. He had helped them as I hadn't.
b. He helped them as I didn't.

c. He had helped them, as I hadn't.
d. He helped them, as I didn't.

Do (a) and (b) mean 'He had helped/helped them in a way that I hadn't/didn't?

Do (c) and (d) mean 'He had helped/helped them but I hadn't/didn't?

 

[Raymott]

a. He had helped them as I hadn't.
b. He helped them as I didn't.

c. He had helped them, as I hadn't.
d. He helped them, as I didn't.

Do (a) and (b) mean 'He had helped/helped them in a way that I hadn't/didn't?
Yes.
Do (c) and (d) mean 'He had helped/helped them but I hadn't/didn't?
Yes.

You'll find that such sentences are normally written less ambiguously.
He helped them in a way that I couldn't.
He helped them where I failed.
Naturally, in speech, you can make sentences like yours mean various things depending on the intonation. They're best avoided in writing.

 

[Tdol]

or because I didn't/hadn't.