Most "better analog scopes have both delayed and "other channel" trigger functions that could well have captured your event.
If you set channel B to trigger on the beginning of a sequence then channel A could be triggered from any event from the channel B source.
I do understand your choice and it was a good one based on your equipment available and the required task.
I frequently use delayed triggering from channel B to either enhance (brighten) a trace on channel A or to simply display the event triggered from the derived channel B event... like the system clock for example.
The point I guess is that because I never had the opportunity to use a GOOD Digital scope, I had to learn to use my "poor" analog scope...
The real issue is that "Digital" is "sexy", most people see digital and a lot of numbers that are SLANTED to make the instrument look good while not displaying the shortcomings of the digital "guts".
The issue really comes back to "What" are you really looking for... faulty code, misused code, faulty design... (typically power supplies and by-passing) or a real issue with a part that isn't performing according to your understanding of the data sheet...
That was my MAJOR area of failure in design... NOT Very Carefully... READING the data sheet... or trying to "Bend" a part to do something not well covered or recommended by the part designer... Mostly I figured out a method to make them work... Because that is "Where the Rubber Meets the Road".
And No one really remembers your successes But NO ONE ever forgets your failures...
Doc