AFAIK, Dan’s page (which I have viewed) doesn’t address this type of issue that I’m mentioning.
If you set a specific negative offset for the current layer (holding the expression) to grab from and there is no positional data at that time-location, then AE simply gives you the position for the current layer before the expression was applied which in this case is nothing.
I’ll try to look at Dan’s page in more detail and see if I can’t solve it that way, but the example that I posted seems to demonstrate the prob, no?
thanks,
f