Credit Card Receivables ABS are backed by pools of rcvbls owed by banks, retailers, travel, and entertainment companies, and other credit card issuers. The cash flow to a pool of credit card rcvbls includes finance charges, annual fees, and prin repmts. Credit cards have periodic pmt schedules, but since their balances are revolving, the prin is not amortized. Because of this characteristic, int on credit card-ABS is paid periodically, but no prin is paid to the ABS holders during the lockout period, which may last from 18 months to 10 years. OAS interpretation depends on sec's credit risk, liquidity risk, and modeling risk relative to the benchmark.
If use Treas secs as the benchmark, the OAS on a GNMA passthru (which carries the full faith and credit of US Govt) reflects liquidity risk and modeling risk. The CMOs themselves issued by GNMA (which are backed by the passthrus) carry additional modeling risk. Also, support tranches carry more liquidity risk and modeling risk than PAC1 tranches, so they should have higher OAS.
Freddie MAC and FNMA secs, which are govt sponsored agencies, also have some small degree of credit risk, so OAS of these secs reflect credit risk, liquidity risk, and modeling risk.
The OAS for non-agency MBS and real-estate backed ABS reflects credit risk, additional liquidity risk to agency-backed MBS, and modeling risk.