Your lawyers don't have any magical insight-- the government of Canada is very transparent about the process on their website, and you can freely check what your score would be using their
online calculator. You can play around with the number of years of work experience that you claim points for to see how it impacts your score.
I would have had a score of 481 if I had listed ALL of my relevant work experience under my NOC in my EE profile. I chose not to list all of it because I didn't need the extra points and wouldn't have been able to get the appropriate documentation from my previous employers anyway. I ended up only listing my most recent job with 2 years of full-time experience, giving me a score of 456. Post-ITA I listed my older work experience in my personal history and explained in my LOE the reason I didn't claim points for it. I never received any ADR. They don't seem to care as long as the work that you ARE claiming points for is thoroughly evidenced.
Alternately, as you sort of alluded to, you do have the option to move work experience from your work experience section to your personal history section post-ITA, but if you do this, your score will be re-calculated post-submission to make sure that it does not fall below the cutoff score for your round. You would also provide a brief explanation in your LOE about why you moved the work experience to personal history. It is not unheard of for people to do this. Work experience that is in personal history does not need to be supported with evidence.