Today went to Big C and got a letter (10 mins/100 baht) and they just updated my passbook without today's deposit entry. 800K approach.
Went to IO at stadium and got an extension of stay for retirement and multi re-entry permit (1900+3800 baht), 90 days report as well.
Passport, copies of used pages, TMs, tm7/tm8 forms completed upfront, 2 photos, banking FD account passbook . 30 mins and out.
No mention of proving 800k later but I know the rules anyways.
They do a very good job.
Hope, this info will be helpful to somebody.
Bob