CSSBusComp verus CSSBCBase

We're using the correspondence table for a custom purpose and tried to use the Correspondence BC oob. We ran into some issues w/ the bc going read-only when the status on our record was "Submitted." Turns out there was some hard-coding in the class and not an editable BC user prop. So, we changed the BC's class to CSSBusComp, which is the default for any new bus comp. Things looked ok for a while until I noticed that my calculated Name field stopped working. As mentioned in the previous post, this uses some calculated fields and the On Field Update BC user props. So I had a hard look at the config, checked VSS for changes (which was extremely tedious) and came across something in Siebel Tools' Help menu. Turns out some user props are limited to certain BC classes. On Field Update is one of those! So, once I changed the class to CSSBCBase, the calculated Name worked again. Additionally, I discovered that for audit trail to work, you must use CSSBCBase. And for those interested, CSSBCBase is derived from CSSBusComp and inherits its properties.