We were recently asked for additional information. First, the Constancia de antecedentes registrales from the PGR (Procuraduría) - this is the national police certificate, not the State one you would have sent earlier and men need either the precartilla or cartilla in order to get it. For those who live in Jalisco, there is now a PGR office in Guadalajara, so no need to go to Mexico City. It's extremely efficient, a whole new generation of people who know what they're doing.
At the PGR, they told my husband about two Mexican men who had had traffic accidents that included some argument over fault and I guess included the police. In both cases, things were settled and they thought that was that. Even so, it appeared in their police history (on the Constancia) and they were rejected by CIC. I'm not sure, but I think an outstanding debt would also count against you and could cause rejection.
You do need to get a certified translation plus enclose the *original* of the Constancia (in one place it says copy, but elsewhere it says original). Make sure you back up all your documents, scan and photocopy.
We were also asked for complete Personal History and Addresses, and they were specific about the periods we had not made clear. When the CIC asks for complete history of activities and work, and addresses, they mean from age 18. Why they confuse things by mentioning the last 10 years I don't know, but that would only be for a quite young person. My husband is 50 and he had to list *and* describe everything he was doing from the age of 18, prep school, university, then all jobs (in Section 8 of Schedule A IMM5669), including the month and year, employer etc. Including a short period when he was not working when his father died. You can't leave gaps, everything has to be consecutive. Same with addresses - speak with family, friends, old colleagues and piece together things that may be vague, but fill it all in leaving no gaps. Pedantic, bureaucratic, whatever, but it has to be done. That includes postal codes. These are things we overlooked in the first place, I don't know how or why, but thank goodness they give us a second chance.
For those who say there are no postal codes, as someone above said about Costa Rica: use Google maps to hone in on your old address or nearby. Find a hotel, restaurant or whatever marked on the map and check it to see how their address is listed, whether there is a code you don't know about or a zone/sector indication. Mexico does have postal codes even though many people wouldn't know their own. If there really is no such thing, I think you should state it clearly - "postal codes are not used", or "do not exist". Just putting "NA" is too vague. They really do want the "i's" dotted and the "t's" crossed.
In Personal History, there is a column that says "status in country" - don't take it for granted, write your status for each and every entry - visa if visiting elsewhere, student visa etc. or citizen if that's the case. Make sure you have all those proofs in your documentation and if you didn't include them earlier (like a student or tourist visa for somewhere else) attach it.
When you pay your fee for right of permanent residence, be sure to email a copy to both Mississauga and to the Mexico office, they provide the email addresses. Not the receipt they send you when you pay - print that out, fill it in with sponsor's name and DOB plus the name, DOB and UCI of your spouse (the applicant), scan that and send that to the email addresses in a format like pdf. Label the top right corner of every page with your spouse's full name, UCI, DOB and we included the application number as well.
What we don't know is whether they will ask for an interview after receiving the Constancia and this last information about Personal History and Addresses. They have the right to, and maybe they do that if there is any information missing still, but they also say in their letter "this is your last chance" to provide the information, so missing anything may cause an automatic rejection.
So these are things we have learned, I hope they may help someone else. We are about to send this package off to Mexico City (by courier of course!). If anyone has any additional information that we might have overlooked, it would be great to hear from you.