Guys, I think there's no point in trying to verify the validity of the "portability before 140 approval" statement anymore. Apparently how a lawyer or immigration officer interpret the AC21 law is a statistical event. What really matters is how USCIS adjudicates this kind of cases in practice. Judging by the articals regarding AC 21 on the 485 boards, the prospect does not appear to be bright. I've read about 485 denials even with 140 approved. It's probably next to impossible to gather accurate statistics on these issues to get a better conclusion. You could always ask your lawyer but whatever advice or data s/he gives you is anecdotal since his clientele is such a minute portion of the vast 140 population. On the other hand, I think we can also forget about a prospect memo. My gut feeling is USCIS's position is an intended strategical ambiguity. They don't want to clearly state a more regic AC21 interpretation which apparently is against the spirit of AC21. Nor do they want to open the flood gate to more problems by publicly adopting a more liberal interpretation.
On this issue, I believe there is no such thing as an "authority". An analogy to this would be trying to find out the weather on a specific date next year. You probably know as much about the topic as your attorney by now.