I've also read that James DeMile mentioned that some people (he specified Joe Lewis on one occasion) didn't think much of trapping and that JD invited JL so that he could demonstrate. DeMile has also said that trapping was a lost art. In the later years, Dan Inosanto said that Bruce didn't even bother to block anymore; it's possible he was alluding that he simply 'intercepted' with a strike. Maybe by this time he dispensed with trapping. But of course, there's no hard and fast rules, so it's also possible BL would use what worked at the moment.