This is a painful area of credit and scoring that no one in the industry wants to really discuss.
In theory, old TLs should remain forever, but there is absolutely no law to help one out and one is totally at the mercy of the CRAs.
There is no law prohibiting the reporting of a positive TL forever, and some like to repeat the industry claim that positive TLs stay for 10 years. But, there's also no law that says a TL has to remain at all for ANY period of time.
You could PIF a car loan, the OC could report the final payment showing the account PIF, and the next day the CRAs could delete it from your CRs and there ain't a danged thing you can do about it.
Reporting at all is in and of itself voluntary. An OC could do a hard INQ for a car loan, CC, home loan or whatever, and then NEVER report at all.
Sucks, don't it?