Do "authorized user" credit cards contribute to establishing credit in the eyes of a credit card issuer?

I found an answer on this forum. Which essentially says an authorized user can help build your credit score but banks ignore authorized user cards when checking if the customer can responsibly manage credit.

If both credit cards were paid off 5 years ago, you would even lack the required credit history to qualify for a 1k loan.

To answer your question, yes. A joint credit card does show up in your credit report and does contribute to your credit score. This is because you are liable for the balance of that card and are responsible for ensuring it is paid. In general, joint credit cards are indicated as such on your credit report, so banks may know that it is a joint credit card.

Whether or not the bank cares about the fact that this is a joint card or not is up to them, though I have not heard of an instance where a bank denies a loan application on the basis of joint credit card history.

However, this is not necessarily the case if you are an authorized user on a credit card (your comment suggests this is your situation), in which case the card may or may not contribute to your credit score/worthiness depending on the policies of the issuing entity. This is because most policies are set up such that authorized users are not (legally) responsible for the balance of the credit card (but are simply authorized to make purchases with it). Thus it follows that being an authorized user doesn't necessarily contribute to proving you are capable of handling credit.

Make sure you're certain of whether you are an authorized user on a credit card or if you are a joint owner of that card. Beyond the question of applying for this loan, being a joint owner has additional implications for your obligations as a credit card holder.

Yes, they do.

Authorized users do build credit. When you become an authorized user, the account is added to your credit report. You can build an excellent credit score just as an authorized user. On-time payments by the primary cardholder will help you build a good credit history.

Yes! They may consider the $30K limit joint credit card until and unless you aren't removed as an authorized user from the joint credit card then the lender would see the $30K Limit.

Becoming an authorized user on someone else's credit card account is a common strategy for improving credit quickly. It works best if the primary user's card has a long record of on-time payments and you as an authorized user don't have any recent blemishes on your credit report.

Make sure that you are not removed as an authorized user form the credit account. Once you're removed as an authorized user, the account may be removed from your credit history. If that happens, any effect the account had on your credit score will be reversed.

until and unless you aren't removed as an authorized user from the joint credit card then the lender would see the $30K Limit.