For "A" lenders, once you receive a "full" approval from them, they do not go back and review documents and redo appraisals. They have issued their full approval. In the situation currently happening, that would be disastrous for the real estate market if that were to be done. I can tell you 100% that there are many homes that were purchased at the height of the market in 2017 where the mortgage financing at the time of closing is way above 100% due to declining values and mortgage insurance premiums. Mortgage insurers do not pull back their approvals in these cases. Where clients get into trouble is when they are rate shopping and do not get all the required documents to the lender so that they can complete their approval process. Once documentation is received and reviewed that opens up the application for further review with the mortgage insurer and lender. Lenders may not order an appraisal until all documentation is received unless the client is paying for the appraisal. Appraised values are Normally not as important on "A" type deals as mortgage defaults for these clients are usually due to non property related issues.
This is all nonsense
There is no such thing as a "full approval"
Period
They will ALWAYS assess the buyer at time of mortgage, consider things like debt service ratios, etc
Even if the house is worth every penny and not over valued, if you did something stupid (eg bought a car 2 weeks before closing) the bank (or private lender) can refuse to give you a mortgage
That paper the bank gives you is pretty clear on terms
You can also view them on website
Oh another fallacy most people believe which is total bs; there is no such thing as a guaranteed renewal either
Mortgage renewal is a privilege not a right
The bank is always allowed to look at your home, your credit etc when deciding whether to extend a renewal