Propane Tank Recertification

I am conducting research on the recertification of propane tanks and have not found any information on the testing procedure used to recertify a tank.
I asked one company to explane how a tank is recertified and received the following reply:
"(1) The tanks are visually inspected for corrosion and mechanical dents and dings.  They are also leak tested (soap bubble test) after filling with propane but they are not hydrostatically tested (using water) because it would be cost prohibitive to do so and it is not required.  (I generally charge $15 per tank for recertification (plus any propane for topping off) if nothing else is required.)

(2) Upon recertification the tank is stamped (using 3/8" high lettering made by a metal stamp) with the month and year following by the letter "E" which shows that it is a recertification by examination.

(3) The above method of stamping the tank is universal and is accepted anywhere.  I have never heard of a situation where a recertification stamp was questioned (although an engraved date would be more likely to be questioned than a stamped date).  However, the propane filling station can refuse to fill a tank based on observed corrosion (regardless of the date stamp)--this happens quite frequently for steel tanks but I have never heard of a case where this has happened for aluminum tanks."
With the above procedure, there is no means to show credibility for the vendor that conducted the recertification test.  Based on my experience with the chemical industry, it would seem that a tank would have to be pressure tested to obtain certification.  If the above test is so simply, any propane filling station could certify a tank by inspection after the tank is filled or anyone with a set of die stamps numbered from 0 to 9 and letter die stamp for  "E" can ..................................
Does anyone have access to a copy of the recertification specifications?
Has anyone recertified a propane tank?
As a side note,  the Overfilling Prevention Device (OPD) specification, which goes into effect April 1, 2002 does not apply to horizontal mounted tanks.